You are the man.

This is fantastic. Can't wait to see how this project progresses.

Some random suggestions:

Maybe I am missing something, but I don't see the ability to add chords outside of the scale. Let's say I want to play an E major chord in an A Minor progression due to a harmonic minor substitution. Is that possible with this tool? It would be cool to be able to add common substitutions or completely random chords too, perhaps in a separate box.

It might also be cool to see the roman numerals along with the chords in the progressions or chord box, but that might be too cluttered.

Regardless, I am an instant fan of this. Great work.