DidiWiki is developed on Linux but reported to work on *BSD's ( including OS X ) and Windows with cygwin. The primary author is Matthew Allum.
MediaWiki
in 85 toolboxes Powerful wiki software built to support the Wikipedia project
PurpleWiki
in 11 toolboxes Wiki with purple numbers, transclusions, and other cutting edge experimental features.
Tiki Wiki CMS Groupware
in 25 toolboxes Tiki Wiki CMS Groupware is a full-featured, web-based, multilingual (35+ languages), tightly integrated, all-in-one Wiki+CMS+Groupware, Free Source Software (GNU/LGPL), using PHP, MySQL, Zend Framework, jQuery and Smarty. It is actively developed by a very large international community. Tiki can be used to create all kinds of Web applications, sites, portals, knowledge base, intranets, and extranets.
Tiki offers a very large number of features "out-of-the-box", arguably more than any other Open Source Web Application. Highly configurable and modular, all features are optional and administered via a web-based interface.
Major features include a robust wiki engine, news articles, discussion forums, newsletters, blogs, file and image galleries, bug and issue trackers (form generator), a links directory, polls/surveys and quizzes, FAQs, banner management system, calendar, maps, mobile version, RSS feeds, category system, tags, an advanced themeing engine (Smarty), spreadsheet, live support, shoutbox, inter-user messaging, menu generator, advanced permission system for users and groups, internal search engine, external authentication support, and much, much more.
