Modular synthesizer
A synth with no fixed signal path: separate modules that the player wires together with patch cables.
Robert Moog and Don Buchla independently built the first commercial systems in the mid-1960s. Moog's approach ran oscillators through filters, the subtractive East Coast school; Buchla on the West Coast preferred wavefolding and complex oscillators, and for years refused to put an ordinary keyboard on his instruments. Everything spoke the same language — control voltage — so any output could drive any input.
Wendy Carlos's Switched-On Bach in 1968 showed what a wall of Moog could do, and how many hours it took. The Minimoog solved that by hard-wiring the patch. The format came back in the 2000s through Eurorack, and in software through VCV Rack.