which uses code that was part of Webcollage. (I couldn't find it now.)

Seriously?

Admittedly there is a company using that name now, but the second google hit points to http://www.jwz.org/webcollage/ JWZs page where he http://www.jwz.org/webcollage/explain.html explains that it's part of most standard distributions of http://www.jwz.org/xscreensaver/ XScreenSaver