Via Isegoria, here is Charles Babbage’s Difference Engine–in high-resolution photography and with a video showing the machine at work. It was designed in 1849 but not actually built until 2002.
The Difference Engine is not a general-purpose computer, but rather was designed for the specific purpose of producing mathematical tables by the method of differences. More about Babbage, the Engine, and the Method of Differences, here.
Fascinating.