The Modulation Path Finder shows how to get from one key to another. Choose the key you are in and the key you want, and it reports how closely they are related, lists every pivot chord the two keys share with its Roman numeral in each key, and lays out several routes: pivot chord, secondary dominant, common tone, through the relative or parallel key, direct phrase modulation, and chromatic mediant for distant keys. Every route plays so you can hear the shift.
It is written for composers, arrangers and theory students who want a modulation that sounds intended rather than abrupt.