Digi-Comp I

The Digi-Comp I was a functioning, mechanical digital computer sold in kit form. It was originally manufactured from polystyrene parts by E.S.R., Inc. starting in 1963 and sold as an educational toy for US$4.99.
A successor, the Digi-Comp II, was not programmable, but in effect a visible calculator. A two-level masonite platform with guides served as the medium for a supply of marbles that rolled down an inclined plane, moving plastic cams as they fell.
Operation.
In essence, the Digi-Comp I contained three mechanical flip-flops, providing an ability to connect them together in a programmable way using thin vertical wires that are either pushed, or blocked from moving, by a number of cylindrical pegs. The whole arrangement was 'clocked' by moving a lever back and forth. Different configurations of these cylinders caused the Digi-Comp to compute different boolean logic operations. With a three binary digit (3-bit) readout of the state of the flip-flops, it could be programmed to demonstrate binary logic, to perform various operations such as addition and subtraction, and to play some simple logic games such as Nim.
Reproductions.
The Digi-Comp I version 2.0 has been made available by Minds-On Toys since 2005 as a relatively inexpensive binder's board version of the original Digi-Comp with a much enhanced instruction manual.