The Mozilla folks, of all people, have launched a simple little multiplayer ‘RPG’ (mostly you fight and get better gear…no stats or levels or anything) called BrowserQuest. Bookmark it for one of those times when you’re sitting in front of your computer bored and want something to occupy your time for 10 minutes. Or two hours. Depends on how compulsive you are.
They created it as a way to show off how awesome HTML5 is. But aside from some guards with the HTML5 emblem on your shields, you’d never know it.