She's a daaaaaaaaaaaaay tripper! One-way ticket, yeah!
Well, now that I've hopefully gotten that song stuck in your head (just please don't tell me you have no idea what song I'm talking about), let's talk a bit about DayTripper, a surreal sci-fi RPG set in the beginning of the 22nd century. The advances in technology in the past hundred years have been pretty momentous. The biggest of which is the "Slip Capacitor" (the second-cousin of the Flux Capacitor) which allows travelers to go into other dimensions and timelines. Great Scott!
There's two main books (the Core Rules and the GM Guide), two modules, and a quartet of supplements available for the game. So you can go and dive headlong into your game. The fellows over there say that each campaign plays more like a collection of one-shot missions, since your characters can't stay away from their "Home-Earth" for more than 24 hours (and I'm sure there's plenty of adventures and situations that bring that time limit to the forefront). So this would be good for a group who might not be able to get together as regularly, or if you've got players who get bored with the "same thing" over and over again.