Apache JSPWiki - Apache JSPWiki is an open source Wiki engine, feature-rich and built around standard JEE components.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
TiddlyWiki - a non-linear personal web notebook
MyPHP Forum - MyPHP Forum is an advanced bulletin board system written in PHP with MySQL as backbone data storage.
Confluence - Confluence is content collaboration software that changes how modern teams work
Niles - A wiki you can talk to