A one-off or small-batch electronic or electromechanical computing machine built before commercial computer production began in earnest, typically a research, wartime or university project rather than a sold product. Belongs here: Atanasoff Berry Computer, BINAC, Colossus, CSIRAC, EDSAC, EDVAC, ENIAC, Harvard Mark I, IAS Machine, JOHNNIAC, Manchester Baby, Manchester Mark 1, MANIAC I, MESM, Pilot ACE, The Bombe, Whirlwind I and Zuse Z3. Does not belong here: a machine that was sold or offered commercially, filed under Commercial Computer, even one built in roughly the same era.