MTS is how you specify how MIDI notes are translated to frequencies, if you desire. You can use it to specify alternative scales, if you desire. The Wikipedia list of hardware and software which supports MTS seems very conservative IMO... my personal experience is that MTS support is reasonably common.
Maybe I wasn't clear when I said "you can use MTS" and "support seems widespread".
It's not part of the base MIDI standard, but it is standardized.
https://en.wikipedia.org/wiki/MIDI_tuning_standard
MTS is how you specify how MIDI notes are translated to frequencies, if you desire. You can use it to specify alternative scales, if you desire. The Wikipedia list of hardware and software which supports MTS seems very conservative IMO... my personal experience is that MTS support is reasonably common.