I'm just getting my place entered here while I think of an idea today.  I will update once that idea come up.  Here is what I do know so far:

It will be in Java (Probably web applet)
It will (at least in the early stages) be a single keyboard multiplayer (2 people on one keyboard)
If time allows I will add network support
More than likely it will be a top-down 2d game.

Let the best game win.