Balder2D is a multiplayer game. It has a networked option and/or players can share a keyboard on the same machine.
Players control small probes which shoot tiny projectiles with which they try to destroy each other. It features a 2D overhead view of the playing field.
It will emphesise team cooperation, instead of the standard frag-fest and meaningless violence of most first person shooters.
As one will not be able to change directions mid flight, one must carefully consider how to get from point A to point B without getting "flashed" (players carry flash pistols which freeze opponants).
For a more I suggest reading the Design Docs, especially the "General description" section.
sudo apt-get install balder2d