Michael Gardi (the same guy who made the Think-a-Dot "computer" toy replica, and the Dr. Nim game replica) made a 3D model of the mechanical Digi-Comp II marble computer so anyone can 3D print one of their own. "I now have the complete collection E.S.R. Inc. products!" says Michael. From his Instructables page: Digi-Comp II is a mechanical computer invented by John Thomas Godfrey and manufactured by Education Science Research (E.S.R., Inc.) in the late '60s.