The Free / Libre / Open Source Web App with the most built-in features
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WackoWiki is a light and easy to install multilingual Wiki-engine.
A web forum written in PHP using a selectable SQL backend
nhnb's Wiki Tools
The Free & Popular MediaWiki Web Software in Complete Virtual Machine
The collection of extensions for MediaWiki software.
Simplest wiki+tracker system
The Halo extension extends MediaWiki and Semantic Mediawiki
MediaWiki extension to create flowcharts from the links between pages.