Walaber's JelloCar has a beta version out. I had to plug in an Xbox 360 controller to get this working, but once going it's weirdly fun. The rubbery car bounces across equally springy terrain, and can occasionally be inflated to pass particularly difficult obstacles. Everything is drawn in lovely scribbled, papery textures.
It's painfully tricky at the moment, but you can see how some really good levels would make this weird wonder play quite beautifully - as a chap notes in Walaber's comments, a checkpoint system for the levels would be useful. I look forward to the finished article.