Probably the most complex mechanical contraption at Maker Faire was the Computer History Museum's model of Charles Babbage's Difference Engine No. 2. Babbage began working on the idea for a mechanical calculator based on the method of finite differences in 1846, but he never actually built the device. The museum showed off a scaled down, table-top model at Maker Faire and demonstrated how it works.
If you're interested in the history of Charles Babbage and his work (both on the Difference Engine and his Analytical Engine, which preceded modern programmable computers), check out James Essinger's book Jacquard's Web. Spectrum editor Tekla Perry will have more coverage when the museum puts the full-size Difference Engine No. 2 on display on May 10th. The machine is 11 feet long and 7 feet high with more than 8000 bronze, cast iron, and steel parts.