WackoWiki - WackoWiki is a light and easy to install multilingual Wiki-engine.
JoinDiaspora - JoinDiaspora is a privacy-aware, distributed, open source social network which are open to anyone.
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.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Hiki - Hiki is a powerful and fast wiki clone written in Ruby.