DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
WackoWiki - WackoWiki is a light and easy to install multilingual Wiki-engine.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
MyPHP Forum - MyPHP Forum is an advanced bulletin board system written in PHP with MySQL as backbone data storage.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
Niles - A wiki you can talk to