The Free / Libre / Open Source Web App with the most built-in features
PukiWiki is used by many users, a light and high functional Wiki clone
nhnb's Wiki Tools
Wiki generator and Java Help System
Open Source Enterprise Wiki and Web Application Platform
The collection of extensions for MediaWiki software.
Make robots for MediaWiki-powered sites!
Emacs extension for interacting with Atlassian Confluence
Web-based knowledge base template.
SuperWikia: The Runtime/Realtime Environment for Codesmiths
KnowWE has moved, please see http://d3web.sourceforge.net