Void
Using nothing more than Newton's three laws and a bit of ingenuity, players attempt to knock each other into the neutron star. The only way to alter the velocity of a ship is to eject mass: remember that for every action there is an equal and opposite reaction. A fun little hot-seat-multiplayer toy.
You can download the source and binaries for Windows. I wrote this way, way back in high school so I make these files available on the condition you don't point and laugh at the code.