I had a funny idea yesterday and patched this today. A four octave keyboard is used to enter new pitches based on the last pitch played and the newest note's distance from middle C.
There's a visualization keyboard above the one used for input.
The yellow note represents the relative pitch you would need to play to return to the note you last sounded. Choosing the green notes seems to return to notes you've played in sequence recently.
It's a bit fun to play.
I wonder if anyone is using a similar scheme with alternative tunings. It might be fun to use with microtonals.