There's a few screensavers included with Haiku, here's your chance to write one as well.

http://dev.haiku-os.org/browser/haiku/trunk/src/add-ons/screen_savers

You can look at the source code of the ones included with Haiku to see what a screensaver needs in order to work on Haiku.  From there it's up to you to add your own flare.  Perhaps a screensaver using the Haiku leaves falling?  Show us what you can do.