via http://education.zdnet.com/?p=2417 "Like Twitter, it’s a microblogging site, but it builds in significant additional functionality to support classroom interactions." "When you create an account, you designate yourself as a teacher or student. Teachers can create groups that students join when they create their accounts (students can join multiple groups and teachers can create and/or join multiple groups); when a group is created, the site generates a group code that must be entered to join. Then, messages, files, links, and assignments can be sent to whole groups."
G. Biegel, и V. Cahill. Proceedings of the Second IEEE International Conference on Pervasive Computing and Communications (PerCom'04), стр. 361--. Washington, DC, USA, IEEE Computer Society, (2004)