This is kind of old news, but news nonetheless
I made a Darkstar based cooperative multiplayer tetris game called Darkstris (pretty original name, huh!).
Darkstris was the grand prize winner of the Project Darkstar Developer Challenge
Unfortunately, it isn't hosted on a server to be able to play it online (the client is a plain old unsigned applet), but since it's open source, you can download it and try it locally (if anyone has a Java server and volunteers to host it, that'll be great)
Feedback of any kind, comments, suggestions, etc is welcome!