Universalis sounds rather interesting. More of a ruleset for roundrobin storytelling than a game system. Or maybe I have that backwards. Worth a look: http://www.indie-rpgs.com/ramshead/
All of the Planescape material any cutter could want, and then some. In addition to many fan-created and non-canon bits, this is the home of the official 3/3.5 conversion of the Planescape campaign setting: http://www.planewalker.com . They have a lovely map of Sigil, of course.
Oh and the ORRIC, a fan recreation of First Edition through the OGL, warts and all:
http://www.knights-n-knaves.com/osric/
