Control your Emacs with an accordion — or any MIDI instrument!
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You can e.g. plug in a MIDI pedalboard (like one in a church organ) for modifier keys (ctrl, alt, shift); or you can define chords to trigger complex commands or macros.
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The idea for the whole thing came from [dead link]. I immediately became totally convinced that a full-size chromatic button accordion with its 120 bass keys and around 64 treble keys would be the epitome of an input device for Emacs.
Well, apparently you can extend Emacs to have it:
https://github.com/jnykopp/emaccordion