KDE has Kwin for 3d effects, and the cube is a part of it. The cube comes with Kubuntu but it's something that I noticed that never really gets talked about. It can be displayed by Ctrl+F11, but I have it set to Super+Z. I think the Compiz cube is a little more configurable though, but the Kwin cube isn't bad either.

For Kubuntu or KDE users, you can configure it at:
settings > Desktop Effects > All Effects > Desktop Cube (and Desktop Cube Animation)