Microscope. It's a storygame which I first learned about through the Diaspora RPG listserv. I have now played it twice. This week's game was particularly fun. We decided to do a game about Space Vikings. Real Space Vikings, the kind who use longships with oars and sails to cross the foamy ether-seas to other worlds.
Our future history (the creation of which is the game of Microscope) began by establishing the beginning era and the end era for our story - the bookends for the timeline as it were. The beginning was the launch of Ragnar's fleet into the ether; the end point was the establishment of a democratic Viking space commonwealth.
The game's mechanics structure play in such a way that players take turns interpolating additional eras between the bookends, and/or specifying events that happen within specific eras. Players can choose to play out certain historical events so that the group can answer a specific question, and determine how historical events moved forward.
So I had an epiphany tonight about how to bring a bit more time travel to the Doctor Who: Adventures in Time and Space RPG. Why not use Microscope to create a world timeline for a campaign? The bookends would be fixed points in time. Maybe what happens between these bookends would be more fluid. Its an idea worth exploring a bit more with the gaming group. Maybe something interesting could come from it.