This is a seriously cool collaborative web2.0 application. It allows you to collaboratively build a mind map online. The tools and fonts are a little limited but the ability to work online with someone else on a brain storm and see their changes as they make them is just brilliant. I've just tried it out and it works brilliantly.
At the moment it is in private Beta testing only but if you want an invitation (and are willing to collaborate with me on something) then send me an email and I'll invite you.
Now to find some people for my class to interact with online. If you have an idea let me know.