DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Apache JSPWiki - Apache JSPWiki is an open source Wiki engine, feature-rich and built around standard JEE components.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
TiddlyWiki - a non-linear personal web notebook
MyPHP Forum - MyPHP Forum is an advanced bulletin board system written in PHP with MySQL as backbone data storage.
XWiki - A powerful Open Source collaborative platform enhancing collaboration and communication.