DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.
Teamemo - Modern wiki software as a service for intranets and knowledge management.
TiddlyWiki - a non-linear personal web notebook
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Scribbleton - The little personal wiki.