FET compressor
A compressor that uses a field-effect transistor as a voltage-controlled resistor, letting it clamp down faster than almost anything else.
Run in its linear region, a FET behaves like a resistor whose value is set by the gate voltage. Wire it as a voltage divider in the signal path and you have a volume control the detector can turn in microseconds. That makes the type well suited to drums and transients, and it adds an audible, slightly aggressive colour when pushed.
The classic is the Urei 1176 from 1967, Bill Putnam's solid-state answer to the tube compressors. Attack goes down to around 20 microseconds, and the knobs run backwards: a higher number means faster. Pressing all four ratio buttons at once was never intended, but it produces a wild, distorted pumping that earned its own name, "all buttons in", and became an effect in its own right.