Three layers of the same image, moving independantly, translucent effects where they overlap, very simple.
With the -rgb flag the images are tied to red, green and blue:
Without it the colours are random:
And there's a short video here (12 seconds, 908k, divx4 format)(windows media player divx4 codec here)
TODO:
Add -circle, -square and -check to generate shapes and -size to customise them. Make the default a random one of these.
I have more screensavers here.