By now this is a little old, but I feel like this is still one of the best and most simple uses of HTML5 to date. And a really good song to boot. You know it's good when you wish you had thought of it first.
From now on, if we find any awesome web apps on the net, we're gonna post it here. Look for awesome sites, hints, games, files, scripts or anything HTML5 or web application related you'll find it here.