So far, my program HARMONY has been enhanced to :

Display guitar or mandolin tab for standard tunings only. It will display multiple voices.

Allow the user to override automatic assignment of notes to strings by entering a specific string for a note.

Save and restore the tune including any overrides specified.

Is that enough to start with?

I plan later to include more instruments (Which ones first?) and to allow custom tunings. This is easy enough to do, but complicates the saving of tunes.