Pressure-sensitive ribbon-controller subharmonic oscillator vacuum tube synthesizer dating back to 1929. “Tongues” can be used for fixed pitches.
I’ve read a lot about early electronic instruments but I think this was new to me. Heard about it from a link someone posted in a Facebook discussion about Hindemith:
Custom-built Trautoniums, including a CV/gate model for use with modular synths:
Detailed technical discussion:
Doepfer Eurorack A-113 subharmonic generator: