Right, that's one.
Anybody want to contribute others?
A motorized trombone line;
A cascade of varactor-tuned 0/pi phase shifters (the ones with the +-1
gain amplifier and the RC lowpass on the + input, or the ones with a
SSB mix with a high frequency tunable oscillator, run the results
through a fixed delay, and mix back down again;
running it through a CCD delay line with a variable clock frequency;
Or even recording on reel-to-reel tape it and slowing the takeup reel
with your thumb.