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. I put up some magic rules I created for my planned elven campaign, and planned to put up some more stuff in terms other Fudge players could use, but I haven't really found the time.
Comment
I would love to see Fudge rise from its online fanbase to gain a wider commercial following. Unfortunately, I think there are problems with the commerical license - on the positive the fee is nominal, but on the negative it does not appear to guarantee that the copyright holder cannot yank the license if he wants (or changes). My full thoughts on how Fudge could become much more commercially successful are laid out in my grandly titled "Manifesto for Fudge becoming Mainstream", on the Fudge Wiki.
Stuff for use with Fudge
I created some rules "The Tale of Fareth and Anriel", a planned elven campaign
Legal note
The Fudge text is copyright Steffan O'Sullivan. In my humble opinion, the information in these pages is compatible with the Fudge text without deriving from it. It therefore does not require a license (Baker vs Selden, 1879). I am happy to give full credit to Steffan O'Sullivan for all the good work he has done writing Fudge, and to link to his Fudge page, but to pretend that my work is a derivation of his when it is not would be no mere courtesy.