There's a ton of background info here: http://rasterweb.net/raster/projects/drawbot/
Basically this is a super-simple Arduino-based robot that uses two continuous rotation servos. The ongoing effort is in the programming of the movement to make it create more interesting patterns.
I'd be happy to work with anyone wanting to build one of these. It's a great beginners Arduino project, and having more than one would mean that more code would be created.