Pick a key, tap a voicing. The keys light up with each note's role in the chord, and it plays so you can hear it land. Triads, extended harmony, the full dominant upper-structure system, and ii–V–I voice leading — in all twelve keys.
Collect voicings as you explore, then print them as a two-handed sheet — every note on a lit keyboard and on the grand staff, left hand and right hand colour-coded.