E.S.R. Digi-Comp I (1963)
The Digi-Comp I was an entirely mechanical digital computer made from plastic parts that could perform Boolean logic operations on a three-digit binary number. And you could have it all for only $5 in 1963.
Users programmed the Digi-Comp to handle simple logical tasks such as addition and subtraction by positioning plastic cylinders at certain points on three plastic flip-flop platforms. Users would then manually slide a plastic plate in and out to perform operations, reading the results on the three-digit counter on the left side of the unit.
The Digi-Comp I was so popular that Minds-On Toys recently released a fully functional cardboard reproduction of the unit that you can buy today.
Photos: Minds-On Toys / E.S.R, Inc.