Have a look at the world from outer space
Sometimes there's nothing more serene at your desktop than watching the world go by - quite literally. Cities of Earth is a majestic free 3D screensaver which shows the most important cities of our planet as viewed from the space. The cities are located according to their actual global coordinates, so the screensaver is also good as an educational tool.
When you run the screensaver, the sunlit part of the Earth is set according to its real time position (calculated from a local time and time zone on your PC). Day gives way to night (and vice versa) very slowly, but if the screensaver is running for a few hours you can witness this. You can also use your mouse wheel to move the camera closer and further away.
The developers say that Cities of Earth saves CPU time for background tasks to run without affecting the rest of your system although we found it was rather heavy on resources.