Edmodo (billed as Twitter for education)
from Mashable Sept 08
Cloud created by:
5 October 2009
"One of the nice features is that students don’t even need an email address to join the classroom. All they need is the special sign-up code that the teacher generates when they create the environment. If a student has already joined another class on Edmodo then they can just log in as usual with their new class assigned to their login".