Administration Apps

Backup

Amanda
Client-server model backup tool
Attic
A deduplicating backup program written in Python
Bacula
Another Client-server model backup tool
Bareos
A fork of Bacula backup tool
Barman
Backup and Recovery Manager for disaster recovery of PostgreSQL servers
Backup
Provides an elegant DSL in Ruby for performing backups on UNIX-like systems
Backuppc
Client-server model backup tool with file pooling scheme
Brebis
A fully automated backup checker
Bup
Incremental backups with rolling checksums, git packfiles, de-duplication, and a FUSE filesystem
Burp
Network backup and restore program
Duplicati
Multiple backends, encryption, web-ui and multi-OS backup tool
Duplicity
Encrypted bandwidth-efficient backup using the rsync algorithm
FreeFileSync
Folder comparison and synchronization tool
Lsyncd
File Monitor which spawns a process to synchronize the changes (rsync by default)
restic
Fast, secure, efficient backup program
Rsnapshot
Filesystem Snapshotting Utility
SafeKeep
Centralized pull-based backup using rdiff-backup
Snebu
Snapshot backup with global multi-client deduplication and transparent compression
UrBackup
Another client-server backup system
ZBackup
A versatile deduplicating backup tool
DREBS
AWS EBS backup script that supports strategies

Build Automation

Apache Ant
Automation build tool, similar to make, written in Java
Apache Maven
Build automation tool mainly for Java
GNU Make
The most popular automation build tool for many purposes
Gradle
Another open source build automation system

ChatOps

CloudBot
The simple, fast, expandable, open-source Python IRC bot
Eggdrop
The world's most popular Open Source IRC bot, designed for flexibility and ease of use
Lita
A robot companion for your company's chat room
Hubot
A customizable, life embetterment robot
Lazlo
A chatops automation framework in Go
KeyBase
Encrypted chat, cloud and git

Cloning

Clonezilla
Partition and disk imaging/cloning program
Fog
Another computer cloning solution
Redo Backup
Easy Backup, Recovery and Restore

Cloud Computing

AppScale
Open source cloud software with Google App Engine compatibility
Archipel
Manage and supervise virtual machines using Libvirt
CloudStack
Cloud computing software for creating, managing, and deploying infrastructure cloud services
Cobbler
Cobbler is a Linux installation server that allows for rapid setup of network installation environments
Tsuru
Tsuru is an extensible and open source Platform as a Service software
Mesos
Develop and run resource-efficient distributed systems
OpenNebula
An user-driven cloud management platform for sysadmins and devops
Openshift Origin
Open source upstream of OpenShift, the next generation application hosting platform developed by Red Hat
OpenStack
Open source software for building private and public clouds
The Foreman
Foreman is a complete lifecycle management tool for physical and virtual servers FOSS
Terraform
Terraform allows you to practice infrastructure as code and is commonly used for AWS/GCE

Cloud Orchestration

BOSH
IaaS orchestration platform originally written for deploying and managing Cloud Foundry PaaS, but also useful for general purpose distributed systems
Ansible
Contains modules for controlling many types of cloud resources
Cloudify
Open source TOSCA-based cloud orchestration software platform written in Python and YAML
consul
It is a tool for discovering and configuring services in your infrastructure
doozerd
Doozer is a highly-available, completely consistent store for small amounts of extremely important data
etcd
A highly-available key value store for shared configuration and service discovery
Juju
Cloud orchestration tool which manages services as charms, YAML configuration and deployment script bundles
MCollective
Ruby framework to manage server orchestration, developed by Puppet labs
Overcast
Deploy VMs across different cloud providers, and run commands and scripts across any or all of them in parallel via SSH
Rundeck
Simple orchestration tool
Salt
Fast, scalable and flexible systems management software written in Python/ZeroMQ
serf
Serf is a tool for cluster membership
StackStorm
Event Driven Operations and ChatOps platform for infrastructure management Written in Python
zookeeper
ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services

Cloud Storage

git-annex assistant
A synchronised folder on each of your OSX and Linux computers, Android devices, removable drives, NAS appliances, and cloud services
nextCloud
Provides access to your files via the web
ownCloud
Provides universal access to your files via the web, your computer or your mobile devices
Seafile
Another Open Source Cloud Storage solution
SparkleShare
Provides cloud storage and file synchronization services By default, it uses Git as a storage backend
Swift
A highly available, distributed, eventually consistent object/blob store
Syncthing
Open Source system for private, encrypted and authenticated distribution of data

Code Review

Gerrit
Based on the Git version control, it facilitates software developers to review modifications to the source code and approve or reject those changes
Phabricator
Code review tool build by facebook and used by WikiMedia, FB, dropbox etc Comes with an integrated wiki, bug tracker, VC integration and a CLI tool called arcanist
Review Board
Web-based collaborative code review tool

Collaborative Software

Citadel/UX
Collaboration suite (messaging and groupware) that is descended from the Citadel family of programs
EGroupware
Groupware software written in PHP
Horde Groupware
PHP based collaborative software suite that includes email, calendars, wikis, time tracking and file management
Kolab
Another groupware suite
SOGo
Collaborative software server with a focus on simplicity and scalability
Zimbra
Collaborative software suite, that includes an email server and web client

Configuration Management Database

Clusto
Helps you keep track of your inventory, where it is, how it's connected, and provides an abstracted interface for interacting with the elements of the infrastructure
Collins
At Tumblr, it's the infrastructure source of truth and knowledge
i-doit
Open Source IT Documentation and CMDB
iTop
Complete open source, ITIL, web based service management tool
Ralph
Asset management, DCIM and CMDB system for large Data Centers as well as smaller LAN networks
Sicekit
The systems & infrastructure encyclopaedia toolkit (based on MediaWiki)

Configuration Management

Ansible
It's written in Python and manages the nodes over SSH
CFEngine
Lightweight agent system Configuration state is specified via a declarative language
Chef
It's written in Ruby and Erlang and uses a pure-Ruby DSL
mgmt
Next generation config management written in Go
Pallet
Infrastructure definition, configuration and management via a Clojure DSL
Puppet
It's written in Ruby and uses Puppet's declarative language or a Ruby DSL
(R)?ex
It's written in Perl and use plain Perl, over SSH without agent
Salt
It's written in Python
Slaughter
It's written in Perl

Continuous Integration & Deployment

Buildbot
Python-based toolkit for continuous integration
Drone
Continuous integration server built on Docker and configured using YAML files
GitLab CI
Based off of ruby They also provide GitLab, which manages git repositories
Go
Open source continuous delivery server
Jenkins
An extendable open source continuous integration server
Spinnaker
Open source, multi-cloud continuous delivery platform for releasing software changes
TeamCity
Powerful Continuous Integration out of the box

Control Panels

Ajenti
Control panel for Linux and BSD
Cockpit
New multi-server web interface for Linux servers written in C
Feathur
VPS Provisioning and Management Software
Froxlor
Easy to use panel for Linux with Nginx and PHP-FPM support
ISPConfig
Hosting control panel for Linux
Sentora
Control panel for Linux, BSD, and Windows based on ZPanel
VestaCP
Hosting panel for Linux but with Nginx
Virtualmin
Control panel for Linux based on webmin
Webmin
Linux server control panel
ZPanel
Control panel for Linux, BSD, and Windows

Deployment Automation

Capistrano
Deploy your application to any number of machines simultaneously, in sequence or as a rolling set via SSH (rake based)
Fabric
Python library and cli tool for streamlining the use of SSH for application deployment or systems administration tasks
Mina
Really fast deployer and server automation tool (rake based)
Rocketeer
PHP task runner and deployment tool
Vlad the Deployer
Deployment automation (rake based)

Diagramming

drawthenet
Draws network diagrams dynamically from a text file describing the placement, layout and icons

Distributed Filesystems

Ceph
Distributed object store and file system
DRBD
Distributed Replicated Block Device
LeoFS
Unstructured object/data storage and a highly available, distributed, eventually consistent storage system
GlusterFS
Scale-out network-attached storage file system
HDFS
Distributed, scalable, and portable file-system written in Java for the Hadoop framework
Lustre
A type of parallel distributed file system, generally used for large-scale cluster computing
MooseFS
Fault tolerant, network distributed file system
MogileFS
Application level, network distributed file system
OpenAFS
Distributed network file system with read-only replicas and multi-OS support
TahoeLAFS
secure, decentralized, fault-tolerant, peer-to-peer distributed data store and distributed file system
XtreemFS
XtreemFS is a fault-tolerant distributed file system for all storage needs

DNS Servers

Bind
The most widely used name server software
djbdns
A collection of DNS applications, including tinydns
Designate
DNS REST API that support several DNS servers as its backend
dnsmasq
A lightweight service providing DNS, DHCP and TFTP services to small-scale networks
Knot
High performance authoritative-only DNS server
NSD
Authoritative only, high performance, simple name server
PowerDNS
DNS server with a variety of data storage back-ends and load balancing features
Unbound
Validating, recursive, and caching DNS resolver
Yadifa
Lightweight authoritative Name Server with DNSSEC capabilities powering the eu top-level domain

Editors

Atom
A hackable text editor from GitHub
Brackets
Open source code editor for web designers and front-end developers
Eclipse
IDE written in Java with an extensible plug-in system
Geany
GTK2 text editor
GNU Emacs
An extensible, customizable text editor-and more
Haroopad
Markdown editor with live preview
ICEcoder
Code editor awesomeness, built with common web languages
IntellijIDEA
Capable and ergonomic IDE, written in Java, It has a lot of plug-ins
jotgit
Git-backed real-time collaborative code editing
Light Table
The next generation code editor
Lime
Aims to provide an open source solution to Sublime Text
SciTE
A SCIntilla based Text Editor
TextMate
A graphical text editor for OS X
Vim
A highly configurable text editor built to enable efficient editing
Nano
A popular text editor, by default comes with most Linux distributions
Visual Studio Code
Fast, hackable, multi-platform code editor from Microsoft

IT Asset Management

GLPI
Information Resource-Manager with an additional Administration Interface
OCS Inventory NG
Enables users to inventory their IT assets
Netbox
IP address management (IPAM) and data center infrastructure management (DCIM) tool
RackTables
Datacenter and server room asset management like document hardware assets, network addresses, space in racks, networks configuration
Ralph
Asset management, DCIM and CMDB system for large Data Centers as well as smaller LAN networks
Snipe IT
Asset & license management software
OpenDCIM
A web based Data Center Infrastructure Management application

LDAP

389 Directory Server
Developed by Red Hat
Apache Directory Server
Apache Software Foundation project written in Java
Fusion Directory
Improve the Management of the services and the company directory based on OpenLDAP
OpenDJ
Fork of OpenDS
OpenDS
Another directory server written in Java
OpenLDAP
Developed by the OpenLDAP Project
Apache Directory Studio
The Eclipse-based LDAP browser and directory client

Log Management

Echofish
A web based real-time event log aggregation, analysis, monitoring and management system
Elasticsearch
A Lucene Based Document store mainly used for log indexing, storage and analysis
Fluentd
Log Collector and Shipper
Flume
Distributed log collection and aggregation system
Graylog2
Pluggable Log and Event Analysis Server with Alerting options
Heka
Stream processing system which may be used for log aggregation
Kibana
Visualize logs and time-stamped data
Logstash
Tool for managing events and logs
Octopussy
Log Management Solution (Visualize / Alert / Report)

Mail Servers

Courier IMAP/POP3
Fast, scalable, enterprise IMAP and POP3 server
Cyrus IMAP/POP3
Intended to be run on sealed servers, where normal users are not permitted to log in
Dovecot
IMAP and POP3 server written primarily with security in mind
Qpopper
One of the oldest and most popular server implementations of POP3

SMTP Servers

Exim
Message transfer agent (MTA) developed at the University of Cambridge
Haraka
A high-performance, pluginable SMTP server written in JavaScript
MailCatcher
Ruby gem that deploys a simply SMTP MTA gateway that accepts all mail and displays in web interface Useful for debugging or development
Maildrop
Open Source disposable email SMTP server, also useful for development
OpenSMTPD
Secure SMTP server implementation from the OpenBSD project
Postfix
Fast, easy to administer, and secure Sendmail replacement
Qmail
Secure Sendmail replacement
Sendmail
Message transfer agent (MTA)

Complete Mail Solutions

Mail-in-a-Box
Take back control of your email with this easy-to-deploy mail server in a box
iRedMail
Full-featured mail server solution based on Postfix and Dovecot

XMPP Messaging Servers

ejabberd
XMPP instant messaging server written in Erlang/OTP
Metronome IM
Fork of Prosody IM
MongooseIM
Fullstack real-time mobile messaging platform (XMPP+REST) in Erlang
Openfire
Real time collaboration (RTC) server
Prosody IM
XMPP server written in Lua
Tigase
XMPP server implementation in Java

XMPP Web Clients

Candy
Multi user XMPP client written in Javascript
Kaiwa
Web based chat client in the style of common paid alternatives

Webchats

Lets-Chat
A self hosted chat suite written in Node

Monitoring Software

Alerta
Distributed, scaleable and flexible monitoring system
Canopsis
Opensource Hypervision and Data Aggregation Software
Cacti
Web-based network monitoring and graphing tool
Cabot
Monitoring and alerts, similar to PagerDuty
Centreon
IT infrastructure and application monitoring for service performance
check_mk
Collection of extensions for Nagios
Flapjack
Monitoring notification routing & event processing system
Icinga
Fork of Nagios
LibreNMS
fork of Observium
Monit
Small Open Source utility for managing and monitoring Unix systems
Munin
Networked resource monitoring tool
Naemon
Network monitoring tool based on the Nagios 4 core with performance enhancements and new features
Nagios
Computer system, network and infrastructure monitoring software application
OMD
The Open Monitoring Distribution
Observium
SNMP monitoring for servers and networking devices Runs on linux
Opsview
Based on Nagios 4, Opsview Core is ideal for small IT and test environments
Riemann
Flexible and fast events processor allowing complex events/metrics analysis
Sensu
Open source monitoring framework
Sentry
Application monitoring, event logging and aggregation
Serverstats
A simple tool for creating graphs using rrdtool (source on github)
Seyren
An alerting dashboard for Graphite
Shinken
Another monitoring framework
Xymon
Network monitoring inspired by Big Brother
Zabbix
Enterprise-class software for monitoring of networks and applications
Zenoss
Application, server, and network management platform based on Zope
Adagios
Web based Nagios configuration interface
Dash
A low-overhead monitoring web dashboard for a GNU/Linux machine
Thruk
Multibackend monitoring web interface with support for Naemon, Nagios, Icinga and Shinken
Uchiwa
Simple dashboard for the Sensu monitoring framework

Metric & Metric Collection

Collectd
System statistic collection daemon
Collectl
High precision system performance metrics collecting tool
Smashing
Ruby gem that allows for rapid statistical dashboard development An all HTML5 approach allows for big screen displays in data centers or conference rooms Fork of Dashing
Diamond
Python based statistic collection daemon
Facette
Time series data visualization and graphing software written in Go
Freeboard
A damn-sexy front-end real-time dashboard Transforms raw JSON into delicious UI
Ganglia
High performance, scalable RRD based monitoring for grids and/or clusters of servers Compatible with Graphite using a single collection process
Grafana
A Graphite & InfluxDB Dashboard and Graph Editor
Graphite
Open source scalable graphing server
InfluxDB
Open source distributed time series database with no external dependencies
KairosDB
Fast distributed scalable time series database, fork of OpenTSDB 1x
NetData
Distributed real-time performance and health monitoring
OpenTSDB
Store and server massive amounts of time series data without losing granularity
Prometheus
Service monitoring system and time series database
RRDtool
Open source industry standard, high performance data logging and graphing system for time series data
Statsd
Application statistic listener

Network Configuration Management

GestióIP
An automated web based IPv4/IPv6 IP Address Management tool
NOC Project
Scalable, high-performance and open-source OSS system for ISP, service and content providers
Netbox
IP address management (IPAM) and data center infrastructure management (DCIM) tool
Oxidized
A modern take on network device configuration monitoring with web interface and GIT storage
phpIPAM
Open source IP address management with PowerDNS integration
RANCID
Monitors network device's configuration and maintain history of changes
rConfig
Another network device configuration management tool
trigger
Robust network automation toolkit written in Python

Newsletters

DadaMail
Mailing List Manager, written in Perl
phpList
Newsletter manager written in PHP

NoSQL

Apache HBase
Hadoop database, a distributed, big data store
Cassandra
Distributed DBMS designed to handle large amounts of data across many servers
Hypertable
C++ based BigTable-like DBMS, communicates through Thrift and runs either as stand-alone or on distributed FS such as Hadoop
CouchDB
Ease of use, with multi-master replication document-oriented database system
ElasticSearch
Java based database, popular with log aggregation, and email archiving projects
MongoDB
Another document-oriented database system
RavenDB
Document based database with ACID/Transactional features
RethinkDB
Open source distributed document store database, focuses on JSON
FlockDB
Twitter's distributed, fault-tolerant graph database
Neo4j
Open source graph database
Couchbase
In-memory, replicated, peristent key/value datastore
LevelDB
Google's high performance key/value database
Redis
Networked, in-memory, key-value data store with optional durability
Riak
Another fault-tolerant key-value NoSQL database

Packaging

fpm
Versatile multi format package creator
omnibus-ruby
Full stack, cross distro packaging software (Ruby)
packman
Full stack, cross distro packaging software (Python)
tito
Builds RPMs for git-based projects

Queuing

ActiveMQ
An open source message broker written in Java together with a full JMS client
BeanstalkD
A simple, fast work queue
Gearman
Fast multi-language queuing/job processing platform
Kafka
A high-throughput distributed messaging system
NSQ
A realtime distributed messaging platform
RabbitMQ
Robust, fully featured, cross distro queuing system
ZeroMQ
High-performance asynchronous messaging library

Relational DBMS

Firebird
True universal open source database
Galera
Galera Cluster for MySQL is an easy-to-use high-availability solution with high system up-time, no data loss, and scalability for future growth
MariaDB
Community-developed fork of the MySQL
MySQL
Most popular RDBMS server
Percona Server
Enhanced, drop-in MySQL replacement
PostgreSQL
Object-relational database management system (ORDBMS)
PostgreSQL-XL
Scalable Open Source PostgreSQL-based database cluster
SQLite
Library that implements a self-contained, serverless, zero-configuration, transactional SQL DBS

Security

Blackbox
Safely store secrets in Git/Mercurial Provides tooling to automatically encrypt secrets like passwords
Denyhosts
Thwart SSH dictionary based attacks and brute force attacks
Fail2Ban
Scans log files and takes action on IPs that show malicious behavior
fwknop
Protects ports via Single Packet Authorization in your firewall
Glastopf
A low-interaction web application honeypot to emulate vulnerabilities and gather attack data
Kippo
A medium-interaction SSH honeypot, mostly used as a standalone SSH daemon with a configurable Filesystem sandbox
OSSEC
OSSEC is a HIDS that performs log analysis, FIM, rootkit detection, and much more
OSQuery
Query your servers status and info using a SQL like interface
pfSense
Firewall and Router FreeBSD distribution
Snort
Snort is a free and open source network intrusion prevention system (NIPS) and network intrusion detection system (NIDS) created by Martin Roesch in 1998
SpamAssassin
A powerful and popular email spam filter employing a variety of detection technique
BounCA
BounCA is a personal SSL / Certificate Authority Key management tool Create self-signed SSL certificates via your browser (Source Code) Apache Python

Service Discovery

Consul
Consul is a tool for service discovery, monitoring and configuration
Doozerd
Doozer is a highly-available, completely consistent store for small amounts of extremely important data
ZooKeeper
ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services

Software Containers

Bitnami
Produces open source installers or software packages for web applications and development stacks as well as virtual appliances
Docker
Open platform for developers and sysadmins to build, ship, and run distributed applications
LXC
Userspace interface for the Linux kernel containment features
LXD
LXD is a container "hypervisor"
OpenVZ
Container-based virtualization for Linux
Docker Compose
Fast, isolated development environments using Docker
Singularity
Flexible containers without root

SSH

Advanced SSH config
Enhances ssh_config file capabilities, completely transparent
autossh
Automatically respawn ssh session after network interruption
Cluster SSH
Controls a number of xterm windows via a single graphical console
Mosh
The mobile shell
parallel-ssh
Provides parallel versions of OpenSSH and related tools
pdsh
Pdsh is a high-performance, parallel remote shell utility
SSH Power Tool
Execute commands and upload files to many servers simultaneously without using pre-shared keys
sshrc
sources ~/sshrc on your local computer after logging in remotely
stormssh
A command line tool to manage SSH connections

Statistics

Analog
Logfile Analyser
AWStats
Generates web, streaming, ftp or mail server statistics graphically
GoAccess
Real-time web log analyzer and interactive viewer that runs in a terminal
Open Web Analytics
Add web analytics to websites using JS, PHP or REST APIs
Piwik
Web analytics application
Webalizer
Fast, free web server log file analysis program

Status Pages

Cachet
An open source status page system written in PHP

Ticketing Systems

Bugzilla
General-purpose bugtracker and testing tool originally developed and used by the Mozilla project
Cerb
Group-based e-mail management project
Flyspray
Web-based bug tracking system written in PHP
MantisBT
Web-based bug tracking system
osTicket
Simple support ticket system
OTRS
Trouble ticket system for assigning tickets to incoming queries and tracking further communications
Redmine
Open source project management/ticketing web application written in Ruby
Request Tracker
Ticket-tracking system written in Perl
TheBugGenie
Ticket system with extensive user rights system

Troubleshooting

mitmproxy
A Python tool used for intercepting, viewing and modifying network traffic Invaluable in troubleshooting certain problems
Sysdig
Capture system state and activity from a running Linux instance, then save, filter and analyze
Wireshark
The world's foremost network protocol analyzer
Trinity Rescue Kit
Linux Live CD for general computer troubleshooting

Project Management

ChiliProject
Fork of Redmine
GitBucket
GitHub Clone written in Scala; single jar install
GitLab
Clone of GitHub written in Ruby
Gogs
Self-hosted Git service written in Go
OpenProject
Project collaboration with open source
Phabricator
Written in PHP
Redmine
Written in ruby on rails
Taiga
Agile, Free, Open Source Project Management Tool based on the Kanban and Scrum methods
The Bug Genie
Written in PHP
Trac
Written in python

Version Control

Fossil
Distributed version control with built-in wiki and bug tracking
Git
Distributed revision control and source code management (SCM) with an emphasis on speed
GNU Bazaar
Distributed revision control system sponsored by Canonical
Mercurial
Another distributed revision control
Subversion
Client-server revision control system

Virtualization

Archipel
XMPP based virtualization management platform
Ganeti
Cluster virtual server management software tool built on top of KVM and Xen
KVM
Linux kernel virtualization infrastructure
OpenNebula
Flexible enterprise cloud made simple
oVirt
Manages virtual machines, storage and virtual networks
Packer
A tool for creating identical machine images for multiple platforms from a single source configuration
Proxmox VE
Complete open source virtualization management solution
QEMU
QEMU is a generic and open source machine emulator and virtualizer
Vagrant
Tool for building complete development environments
VirtualBox
Virtualization product from Oracle Corporation
Xen
Virtual machine monitor for 32/64 bit Intel / AMD (IA 64) and PowerPC 970 architectures

VPN

OpenVPN
Uses a custom security protocol that utilizes SSL/TLS for key exchange
Pritunl
OpenVPN based solution Easy to set up
SoftEther
Multi-protocol software VPN with advanced features
sshuttle
Poor man's VPN
strongSwan
Complete IPsec implementation for Linux
tinc
Distributed p2p VPN
wireguard
New minimal VPN Solution that is very fast

Web Servers

Apache
Most popular web server
Caddy
The HTTP/2 Web Server with Fully Managed TLS
Cherokee
Lightweight, high-performance web server/reverse proxy
Lighttpd
Web server more optimized for speed-critical environments
Nginx
Reverse proxy, load balancer, HTTP cache, and web server
uWSGI
The uWSGI project aims at developing a full stack for building hosting services

Web Performance

HAProxy
Software based load Balancing, SSL offloading and performance optimization, compression, and general web routing
Squid
Caching proxy for the web supporting HTTP, HTTPS, FTP, and more
Traefik
Træfɪk is a modern HTTP reverse proxy and load balancer made to deploy microservices with ease
Varnish
HTTP based web application accelerator focusing on optimizing caching and compression

Webmails

Mailpile
A modern, fast web-mail client with user-friendly encryption and privacy features
Roundcube
Browser-based IMAP client with an application-like user interface
SquirrelMail
Another browser-based IMAP client

Wiki Software

BookStack
A simple, user-friendly wiki built with PHP that uses MySQL for storage
DokuWiki
Simple to use and highly versatile wiki that doesn't require a database
Gollum
A simple, Git-powered wiki with a sweet API and local frontend
ikiwiki
A wiki compiler
MDwiki
Wiki completely built in HTML5/Javascript and runs 100% on the client
MediaWiki
Used to power Wikipedia
MoinMoin
An advanced, easy to use and extensible WikiEngine with a large community of users
Ōlelo Wiki
A a wiki that stores pages in a Git repository
TiddlyWiki
Complete interactive wiki in JavaScript