Very well done. Looks and sounds great.

A couple of UX thoughts I had while using it:

1. Since the chords are all within a specific key, have you considered using the numbers 1 through 7 to play the respective chords? That way playing a 1-4-5 or a 2-5-1 would be very intuitive?

2. Have you considered using modifier keys (shift, ctrl, alt) to control whether a chord is strummed down versus up (e.g. pressing A would be down, but Shift+A would be up) or major/minor (A would be major, Alt+A would be minor)? I guess Ctrl could be a 7th chord modifier too.

Just some thoughts. Great tool!