UI Recipes - Weekly 15 min lessons on UI design from the hottest apps
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
UI Movement - The best UI design inspiration, daily
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Design Principles - An open source repository of design principles and methods
Confluence - Confluence is content collaboration software that changes how modern teams work