The only time I want to run the Tomb of Horrors is with this game.

This great! My friends and I had a blast and created a really cool city! Floating churches, fey spies, and overgrown automata! 

A very charming little collaborative world building game, that takes Microscope and dramatically improves it. If, like us, you thought Microscope was a bit too high-level and too restrictive, Street Magic may be the game you're looking for!