This post on Story Games I find quite exciting. A month to design a game, using a previously published system? And the additional commitment of having to also be a judge.
As a commenter on that page put it:
"It's the exact same situation as Game Chef or 24 hour RPG -- feel free to draw on old material, but the contest is about writing and presenting new stuff, not dusting off your hoary old setting."
I'd love to do this. But do I have the time?