Saw this on BoingBoing :

Mario Level Editor

A level editor for Super Mario World. Crazy. More fodder for the Mame crowd. Awesome. One of these day’s ill get around to getting emulators on my PSP. But I’m just lazy

Lunar Magic is a level editor I created for Super Mario World (SNES). It’s the first and, as far as I know, the only level editor available for this game. I began looking into making an editor for it shortly after releasing the SoM VWF patch, mostly on a whim to see how hard it would be. It wasn’t intended to be a long term project, but things would turn out otherwise…

P.S. First person to make a whole new super mario world gets a cookie.
P.P.S. Note that I made some new categories. Emulation and Custom Gaming.