Announced back in August, Mari0 — a full game of Super Mario Bros. played with a Portal gun — has released, and it offers way more than what its premise suggests. The game just became available minutes ago by its makers, StabYourself.net
The video above shows you all that you get, but my advice is to simply download it and try it out for yourself. There are versions for Windows, Linux and Mac OS, plus the game's original source code, for free at the link.
With it, you get four-player simultaneous cooperative play, a level editor, downloadable map packs, game modifiers like giant-size Mario or super-floaty physics and even 33 different hats. What are you still reading me for? Go get it! Go on!