MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Pmwiki - PmWiki is a wiki-based system for collaborative creation and maintenance of websites.
TiddlyWiki - a non-linear personal web notebook
MDwiki - Static single file CMS/Wiki done purely with client-side Javascript and HTML5.
Confluence - Confluence is content collaboration software that changes how modern teams work
Ema Personal Wiki - Ema Personal Wiki uses Markdown to freely create and manage structured notes, like a website.