A friend of mine from college is working on this and I think it's quite cool: a foldable, stackable electric car. It's a little reminiscent of a grabbing a shopping cart -- the idea is that you rent these cars point to point, instead of taking roundtrips like you would with programs like Zip Car or City CarShare. Because the cars pack more densely, you can keep a greater supply of them within a city. Six to eight cars will fit in a conventional parking space -- considering that space for parking is on the order of $thousands/space, that's a lot of extra savings that the program could work with.

cities.media.mit.edu, Tech Review article has more