I fell into some kind of HTML 5 Canvas documentation trance and fell out of it a few hours later with a primitive little game demo, which I hereby dub FlatRoller (source on GitHub):
Gameplay is basically a 2-d side-scroller version of Katamari Damacy, with … not a lot of complexity. Roll your giant ball of stuff left or right and collect stuff to build it up to a larger size! And you can jump. Sometimes you bang into things.
Tested in current releases of Firefox, Chrome, Opera, and Safari, as well as Mobile Safari on iPad. Not tested in Internet Explorer, though IE 9 and 10 should work in theory. Physics are pretty crap, and it doesn’t do wrapping on the play area quite right… and of course it looks like I scrawled the graphics in MS Paint (actually Gimp ;)
But it is kinda fun; I think I’ll clean this up and use it as an example in tutorial documentation for VCS stuff and of course for gfx-heavy web thingies…
Interactive widgets and mini-games/applets using the same sorts of tech are a big potential for online reference and educational media — in particular bringing authoring environments into the wiki or other on-web whatsit should make some really cool projects and learning tools possible.
Update 2011-11-20: Size & multitouch tweaks
Maybe have a look at http://gamejs.org/ :-)