As reported by Creative JS, Jasmine Kent ported her open source Linux racing game Trigger Rally to WebGL to run in HTML5 browsers. In the following video you can see it running pretty smoothly on my MacBook air that is already running 12% of CPU without it starting (as ScreenFlow is recording and VLC was playing music whilst TweetDeck used quite a chunk, too):

If you are the artistic type, you can even design your own levels for the game.

You can play play Trigger Rally online here: http://triggerrally.com/ or follow it on Twitter @triggerrally.