Wikipedia's underlying open source wiki engine.

A kitchen-sink content management system that combines wiki with a Slashdot-style article system, blogs, forums, image galleries, chat, and so on. Pear:DB backend, LGPL.

Feature-rich implementation with support for various databases.

A free PHP/MySQL wiki engine based on forked code from WakkaWiki, with a number of features beyond the original Wakka, including a GUI page editor, advanced syntax highlighting and mindmap support. Released under GPL.

A simple-to-install system which allows password protection and organization of pages into groups (GPL).

Popular extension of Wikipedia's wiki engine with Semantic Web features, enabling better search and organization of wiki content.

A PHP script that runs wiki sites.

Open source wiki, based on Wakka Wiki, enhanced (XHTML 1.0 and CSS compatibility) and translated into French.

Wikepage is an easy to use and small dual-mode wiki engine that can act as wiki sites and personal homepages.

Open source wiki engine written in PHP for the Midgard Content Management System.