site (http://www.fullscreenmario.com/) (while it's still up), github (https://github.com/Diogenesthecynic/FullScreenMario)
It's Mario! On your browser! In JavaScript+HTML5! And open-sourced!
While according to the Reddit thread it's already been C&D-ed by Nintendo, it's meant as a completely editable Mario-style platform engine and the main reason the creator used Mario is to show people it was possible. In the project's GitHub issue tracker he says he can always replace the media resources used if/when Nintendo jumps on him.
MEANWHILE: THIS would be exactly what we could use (minus the Mario resources) as the platforming tech demo for Sphere if we could get it sufficiently edited as such.
That's pretty cool (although really, really slow for me).
It's too slow and not quite accurate to the Mario games (I played a lot of Mario in my youth), though I do like the fact that it's otherwise a pretty solid game using html 5 and JS. And it's pixel art is nicely upscaled, which is great since it's not always easy to do that.