Multi-layer Tron. Each layer is a different height and different shade of gray. You can move up and down within these layers, going under trails instead of around them.

I haven't really thought this through.

That would be epic. Last-minuete contest entry, anyone?

The basic gameplay of Spacewar! involves two armed spaceships called "the needle" and "the wedge" attempting to shoot one another while maneuvering in the gravity well of a star. The ships fire missiles that are unaffected by gravity (due to a lack of processing time). Each ship has a limited number of missiles and a limited supply of fuel. Each player controls one of the ships, and must attempt to simultaneously shoot at the other ship and avoid colliding with the star. The hyperspace feature can be used as a last-ditch means to evade enemy missiles, but the reentry from hyperspace would occur at a random location and there is an increasing probability of the ship exploding with each use.