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