SaverLab runs Mac OS X screensaver modules in regular windows. It allows you to run any number of modules simultaneously, pause, single step, and save animations as QuickTime movies, and allows you to use a screensaver as your desktop background (see documentation for details and limitations).
RORO01 Only one problem - "Full Screen" is not as it's name suggest but it is in fact full screen window. This is significant when you set System Preferences/Energy Saver/Sleep to put the display to sleep when inactive for a specified amount of time. In full screen - as opposed to full screen window - the display doesn't go to sleep. (Version 1.7.4)