Comment by lproven

« Not random 3d objects bit 2D compatible abstractions similar to windows that render what would be a window on one face for regular apps but for 3d apps, different faces and relationship between cubes can be configured »

Sun's "Project Looking Glass" did some of this.

https://en.wikipedia.org/wiki/Project_Looking_Glass

It's the only windowing environment I have seen that uses the fact that windows have 2 faces: the front holds content, the back holds config.

It was a clever design but it didn't get far.