http://idea.live.com
Windows Live. Generally an online verson of Windows. They have a bunch of stuff celebrating it. However. It is all BETA. As is Win Live itself.You need invites for individual applications because:
A. You must be authourized to use this software.
B. They do not want anyone leaking information.
You might want WLM (Windows Live Messenger) because it has shared file system and Offline messaging.