Galactix is a single-player overhead spaceshooter mod that's had a lot of people asking "This is Quake?!" The point of the mod is to kill enemies and collect points in order to get the high score. You have to dodge quite a few asteroids, and a number of ships weilding a variety of deadly attacks. Luckily your ship is no pushover. You can choose from 3 distinct ships, each boasting a different attack type and different missiles. Collecting powerups will upgrade the weapons you have, give you missiles, heal your health, or give you bonuses.
Also be sure to grab CheapHack to play it with.