BumpTop, a 3D desktop interface for Windows, is now available for download in a free and $30 "Pro" version.
I just dinked around with it for five minutes. It's amusing, and perhaps even fun, but it feels a little primitive to me for some reason. It might the sheer boxed walls.
Still, it's free, and this sort of thing can't be assessed in five minutes. You have to get around inside and spend some time with it. And if you had a touchscreen machine, I could see it being a lot more fun. Icons + physics is a hoot.