Do you like graphics gizmos on your desktop? Here is one you should try. The time cube displays a small rotating cube, displaying the current date and time, directly on your desktop. OpenGL is used for quite some special effects: specular highlights, realtime bumpmapping und cube map reflections.

The cube is partially transparent, so you can see the window contents behind it (sometimes you have to look closely though). It can be dragged around on the desktop with the left mouse button.

More info and download:
Time Cube 1.0