MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Documize - Enterprise-grade wiki and knowledge management platform
TiddlyWiki - a non-linear personal web notebook
Boardist - Personal workspace for all the data
Confluence - Confluence is content collaboration software that changes how modern teams work
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.