I’m guessing that the screen savers themselves doesn’t need any introduction. Many people like the Mystify, Ribbon or Bubbles screen saver, but secretly wish they could tweak them, ever so slightly. Having just one mystify ribbon scrolling over your screens – it seems lonely. Having a small monitor, the bubbles get too big.
Word has it that the people behind the screen savers did intend to add a settings menu to them, but never got around to it. Nevertheless, they all come with a few hidden settings that you can tweak.