ELGG
ELGG is a social software system that has gained quite a lot of attention in the educational community. Elgg is an open source social networking platform developed for LAMP (Linux, Apache, MySQL, PHP) which encompasses weblogging, file storage, RSS aggregation, personal profiles, FOAF functionality and more.
In education it could be used for e-learning 2.0 scenarios and personal learning environments.
Features
(There is also a bigger picture, but it seems to be corrupted)
ELGG features include: Blogging, Social networking, File repositories for individuals and communities, Podcast support, Full access controls, Supports tagging, User profiles, Full RSS support, RSS aggregator, Create communities, Collaborative community blogs, Create 'friends' networks, Import content, Publish to blog, Multilingual, Branding/customisation