Two days ago a new version of the free 1st-person-shooter Cube has been released.

Cube is an open source multiplayer and singleplayer first person shooter game built on an entirely new and very unconventional engine.

I haven’t played it online yet but offline it’s really a funny game :-) It’s more like SeriousSam/Quake/Doom than Counterstrike and co. but if you just want to make a quick session it’s perfect :-)