The Digi-Comp I is a functioning, mechanical 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 $5.95.
In essence the Digi-Comp I contains three mechanical flip-flops and provides 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 is 'clocked' by moving a lever back and forth. Different configurations of these cylinders cause the Digi-Comp to compute different boolean logic operations. With a three binary digit readout of the state of the flip-flops, it can 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.
The Digi-Comp I version 2.0 was made available by Minds-On Toys in 2005 as a relatively inexpensive cardboard version of the original Digi-Comp with a much enhanced instruction manual.
A successor, the Digi-Comp II, is much more elaborate. A two-level masonite platform with guides serves as the medium for a supply of marbles that roll down an inclined plane moving plastic cams as they go.