HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.
TiddlyWiki - a non-linear personal web notebook
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Confluence - Confluence is content collaboration software that changes how modern teams work