Conversation so far:
What is the fingerboard controller?
Fingerboard-controlled instruments include the Trautonium (1929), Hellertion (1929) and Heliophon (1936).
Who used these intruments?
Rock musician Keith Emerson used it with the Moog modular synthesizer from 1970 onward.

Question: Did any other artists use it?
Self-contained rewrite: Did any other artists besides Keith Emerson use a fingerboard controller?