HowHive - Knowledgebases for teams and companies of all sizes. Knowledge sharing and finding made simple.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Raneto - Open source, flat-file Knowledgebase platform that uses static Markdown files
TiddlyWiki - a non-linear personal web notebook
openKB - openKB is a Markdown Knowledge base application (FAQ) built with Nodejs and ExpressJS.
Confluence - Confluence is content collaboration software that changes how modern teams work