We have just realeased a new version of Social Stream, a Rails 3.1
gem that provides web developers with a powerful engine for building
SocialStream currently supports users and groups, as well as posts,
attachments, pictures, audios and videos with HTML5 support. We are
working on videoconferences.
SocialStream is Rails engine, so every part of the gem is customizable.
also modular. Check it out at http://social-stream.dit.upm.es/