MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
XWiki - A powerful Open Source collaborative platform enhancing collaboration and communication.
TiddlyWiki - a non-linear personal web notebook
Confluence - Confluence is content collaboration software that changes how modern teams work
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
BookStack - An open source knowledge management application that's focused on ease of use.