Compiz is Window Manager that has special effects. Now merged with Beryl into Compiz-Fusion, but still available as Compiz Core, without Fusion additions.

More Window Managers with Special Effects
How to Change Window Manager

Compiz homepage
wikipedia page
Puppy Lucid 5.28 + Compiz thread
Compiz on Ubuntu (1 min 36 secs)
List of window managers