Fudge, by Steffan O'Sullivan and members of rec.games.design, is a brilliantly simple core ruleset for storytelling games. With more optional rules either in rule books and around the web than a Superb quarterstaffer could shake a stick at. There is a good set of links to get started with Fudge at the Phoenyx Fudge page, and the main Fudge publisher Grey Ghost Games has a site which includes the full downloadable text. I put up some magic rules I created for my planned elven campaign, and will put up some more stuff in terms other Fudge players could use if and when I create it for my game.
My thoughts on how it can fulfill its potential, as an open community project, are here "Manifesto for Fudge becoming Mainstream". I also put William Stoddard's writeup of his 1920s superheroes story, Gods and Monsters on the same Wiki.
I created some rules "The Tale of Fareth and Anriel", a planned elven campaign
The Fudge text is copyright Steffan O'Sullivan. These pages are compatible with the Fudge text without deriving from it.