The Social Media Classroom is a new project started by Howard Rheingold which offers an open-source Drupal-based web service to teachers and students for the purpose of introducing social media into the classroom. The service includes tools like forums, blogs, wikis, chat, social bookmarking, RSS, microblogging, widgets, video conferencing, and more.
In the short time that I have used it, Twitter has grown quickly to play a major part in the way that I interact with fellow colleagues and professionals from around the world.