The late, lamented Hubris Games published a line of remarkable line of roleplaying game materials, starting with Maelstrom Storytelling, that combined an innovative roleplaying system with interesting setting material, producing along the way the introductory Story Bones and and the universal roleplaying game engine Story Engine. Ron Edwards’ review has a good description of both Story Bones and Story Engine.
Hubris Games’ website unfortunately disappeared sometime in 2003, so I’ve made a few of the free downloads from their site available on this page.