TiddlyWiki - a non-linear personal web notebook
WackoWiki - WackoWiki is a light and easy to install multilingual Wiki-engine.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.
wikidPad - wikidPad is an application for storing thoughts, ideas, todo lists, contacts, or anything else that user can think of to write down.