This is a midi effect that outputs a four-note diatonic chord according to the key you play.
It’s a variation of a patch I made previously called Diatonica (https://patchstorage.com/diatonica/), but I made it more practical.

It accepts inputs from C2 to C4.
Velocity is available.
The keys are displayed on the circle of fourths.
You can choose from major, natural minor, harmonic minor, and melodic minor scales.
It outputs the diatonic chords for each scale.

You can play diminished chords on the black keys of major and natural minor scales.

The II-V section outputs the subdominant and dominant of the root note you press.

Each note can be shifted, and then it goes to the voicing section.
It controls chord inversion and voicing of 4 midi notes.
https://patchstorage.com/4voicing/
1,3,5,7 can be muted.
In single voice mode, you can select the constituent notes of the chord from the bottom up and play single notes.
Chords and single notes can be switched ON and OFF with the knob.
Finally, it goes through the MIDI humanizer.

NOTE : I released this patch previously but it only worked in the beta version. I fixed the bug and it should work fine now.