Bloomfire - Let Bloomfire help you get organized! Organize your content, build your company knowledge base and help your employees to be more successful.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Confluence - Confluence is content collaboration software that changes how modern teams work
Tiki Wiki CMS Groupware - Tiki Wiki CMS Groupware, also known as Tiki (or TikiWiki), is a full-featured, web-based, multilingual, all-in-one Free/Libre Open Source Software solution. Tiki can be used to create all kinds of web apps, portals, knowledge bases, intranets, etc.
Tettra - Tettra is a company wiki that helps teams manage and share organizational knowledge.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.