MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
AMuseWiki - Amusewiki is more than just a wiki engine, it’s also a powerful authoring, archiving and publishing platform.
Pmwiki - PmWiki is a wiki-based system for collaborative creation and maintenance of websites.
BetterDocs - Create & Manage Knowledge Base Documentation Effectively To Reduce Support Tickets, Increase productivity & User Experience with BetterDocs.
PukiWiki - PukiWiki is a functional and reliable wiki software that has been widely using for Japanese wikis and is using the PHP framework.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.