Crossbar switch
Telephony's grid of crossing bars with a contact at every intersection — a topology that outlived the exchange and now sits inside chips and switches.
The design is Swedish. Gotthilf Betulander of the Swedish Telegraph Board patented the principle in 1919: horizontal and vertical bars in a matrix, with an electromagnet at each crossing able to close the path between one incoming and one outgoing line. Any input reaches any output, and the connection is made in milliseconds without a selector stepping through every intermediate position. AT&T took up the idea and put its No. 1 Crossbar into service in 1938.
Computing met the component almost immediately. George Stibitz's Complex Number Calculator at Bell Labs in 1940 used crossbar switches as storage for its intermediate results. That was no accident: telephone parts were designed to switch reliably between defined states and could be ordered by the crate, which is roughly the entire requirements list for digital electromechanics.
The price is that cost grows as inputs times outputs. A full matrix becomes unmanageable as soon as the port count rises, which is why telephone networks were built in stages and why modern switches use Clos networks of smaller matrices. The topology itself lives on in switch fabrics, memory interconnects and the networks between cores on a die, where crossbar still means exactly what Betulander drew.