There's quite a few jazz things that are missing. E.g., altered and bebop scales, 7#9 and 7b9 chords. Plus, for any given chord, there are a lot of voicings (drop 2, rootless, etc.).

This suite could be a really cool resource for new/intermediate jazz guitarists if you add some of the jazz stuff in. Any decent jazz guitar book could give you the most used scales and chord voicings.

Since the UX is already quite good, maybe if you open source it and if these things are easy to add, you could rely on the community to do so to some extent.

I like the UI though, and the omnipresence of the metronome is cool.

Consider adding a playback feature for the chord progressions as well as the musical modes, so people who are unfamiliar with certain ones can get a feel for how they sound.

Also any particular reason for naming it after the FF6 yeti? :)