Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
EduDo - EduDo is a video discussion platform
Textpattern - Textpattern is an elegant content management system that is free, open source software.
TeenUp - A learning platform designed for teens by teens
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
PalPark - Curate and share your learnings by topics