Dio is a new interactive tool from Linden Labs, the creators of Second Life (which, apart from hearing from people with physical disabilities that it was very helpful to them, I have yet to figure out its usefulness).
Dio, on the other hand, allows you to create what is basically a public or private network that has a lot of interactivity. There is no shortage of social network sites that teachers can set up for their students to use (see Not “The Best,” But “A List” Of Social Network Sites), but Dio seems to have a lot more engaging features. Let me know if you see other educational uses for it.
It’s in beta right now, and you need an invitation to join. However, I received one seconds after my request. Here’s a their video: