Brent Thome, a computer scientist in San Francisco, is building a mechanical computer out of beautiful, laser-cut gears that will compute and draw fractals. He's documenting as he goes in a fascinating blog, in which he also recounts his adventures with kinetic wooden sculpture.
I've been working on this for a while now. Its a wooden computer that computes continuous self-similar fractals. I'll post the working model of a general computer implemented in gears as soon as I get some laser cutter time to complete the counter/comparator unit. Anyway, here is some pictures of the core assembly.
This prototype of the core stands about one meter tall. The final version of the core will stand over two meters tall and is one of three subunits that preform calculations, logic operations, and store/load values.
Below is the disk drive. It literally turns disks with lookup tables, each with a 96 bit capacity. The disks are not shown here.