Cyborg Rage, a shmup with procedural enemy generation similar to how Left 4 Dead does it, is now available on Steam. After its beta last November, the game cleared Steam Greenlight and is now available for full purchase.
Two players can team up online to battle their way through the hordes of "Battle Cyborgs." There are three ships from which you can choose - the heavy Alpha Class, the speedy Delta Class, and the special weapon focused Beta Class - and pair up in order to take full advantage of each one's strengths. Each ship's arsenal can be determined before kicking off the firefight, and there is some degree of ship progression/leveling.
Cyborg Rage is available for $4.99 on Steam.