The category of one-of-a-kind computers contains computer systems of which only one unit was ever produced due to the particular system's state of being an experimental prototype and/or because of its massive size, complexity and cost. Among those systems are the pioneering electro-mechanical and electronic computers made in the 1930s, 1940s, and 1950s, and, after that period, the largest supercomputing systems.

See also Category:Cryptanalytic devices

History of computing | Classes of computers