Quake III Arena 188.8.131.52
In the demo, you can play single-player against the bots or multi-player over a server, with a set frag limit or time limit.
There are male and female skins to choose from when you set up your player.
While you're playing, you'll want to collect health bubbles and armor to become stronger as you face your enemies. There is also Quad Damage with which you can destroy just about anyone, as long as you can stay on your feet.