Below, you'll find my first experiment using the HTML5 <canvas> element. I've re-created one level from Lights Off, an old (native) iPhone game that I really enjoyed. Since it uses the <canvas> element, only modern browsers will show the game.
Simply click on an area, and see all the surrounding lights turn on or off. Your target is to get all the lights out, good luck!
I know the design could be improved and stuff could be added (high score, timer, more levels), but this is just an example to show some features of the <canvas> element.