One of the games I played A LOT before i became so totally swamped in the awesomeness of Toribash was Garry's Mod (GMod for short). It's a really cool physics simulator that allows you to spawn various items and make contraptions from them such as turrets or spaceships or... or... GIANT... MECHANICAL...ZOMBIE KILLING ROBOTS? >.>
Anyway, hit my thread if you play. If you don't, I highly recommend you try it.