Local chord analyzer
This feature could be an enablable button within the "Client Settings" tab. It could read out simple to advanced chord / note names in the empty space shown in the image below.
Even an option to toggle between local and global analyzation (seeing everyone's chords / notes) could be fun. Though the way I could see global analyzation working out is in two different paths:
A: The chords / notes someone else is playing could be displayed by that person's cursor nametag or could show up as
at the same time, pile on each other, then disappear once the chord is no longer held down.
B: The chords everyone is playing overwrites each other on your local display. (Maybe a small delay between chord changes to not cause epilepsy)
I could see this as a great opportunity for the users / community to learn chords, scales, structures, their favorite songs, and much more in a simple way through their favorite piano site.