This page has various things which one could consider existing in the physical world (as opposed to Software).
The CARDboard Illustrative Aid to Computation was a cardboard computer created by Bell Labs to teach students the basics of computers. The computer doesn’t actually do arithmetic for you but instead leads you around a flowchart to keep track of the state of a loaded program. There is more information about this on Wikipedia.
I made my own version of it from the few pictures I could find on the Internet in 2005. It is fairly easy to build, with the main difficulty being cutting rectangles out of the center of the paper. I would recommend printing the sheets on card stock for durability (I think I used 110 lbs).
Here are PDF files to print and assemble:
|Arithmetic logic unit
A few years after creating my own CARDIAC, someone sent me scans of an actual CARDIAC along with the guidebook! I’m posting these here for posterity.
Surprisingly, it looks like you can still buy an original CARDIAC, for instance at Scientifics Online.