So I saw this on Joystiq a couple days ago and wow, this is awesome. http://stabyourself.net/mari0/ Using a 2D gaming engine that uses Lua called Löve, this guy/these guys have re-created NES Super Mario Bros and have given him a portal gun. There appears to be a real-time map editor and all sorts of portally goodness mappacks that they're adding all the time. It's absolute genius and you ought to check it out. The best part is, the Löve platform has been developed for Windows, PC, and Linux! A great set of animated screenshots that show what they've accomplished already ... like these: