Beats Plasma Pong if you ask me.
You use motion physics to kill your enemy
Only the trial version is free, but it's not really limited. You can't save your replays, and you can't play on the full servers, but there are plenty of demo servers.
You have to really experiment, though. I mean I've found that various muscles do things you wouldn't expect. I've also managed to rip my opponents head off while grabbing his right arm with my right hand and pull at the left side of his face with my left hand xD
Remember to use the Glutes for help in jumping, along with ankles. And use your pecs along with your shoulders and torso to throw punches. Just using your arm by itself will only result in busting yourself in the face...or sadly enough, ripping it off like I did once.
I've actually seen players rip off their own limbs and beat others with em. xD
