Drempels makes colorful, swirling, hallucinogenic patterns that resemble a hurricane or tornado. It normally runs in your Windows background or "desktop", replacing your old still-image wallpaper with gently-animating visuals... and meanwhile, you can use your computer just like you normally would. It uses very little CPU overhead - so little that it even runs smoothly on a 233 MHz system!
Drempels can also be used as a screensaver; in this mode, it goes fullscreen (like a normal screensaver) instead of rendering to the desktop/background.
Drempels works on Windows 9x, ME, NT, and 2000. It requires DirectX 5.0 or later and an MMX-capable processor.