Chopin used a technique of moving between chords that didn't depend on functional harmony but on chromatic closeness. The chords would gently fold chromatically into each other, and it "worked" because the chords shared notes in common and the other notes voice led gracefully. I've also seen a few jazz compositions that work similarly. This app was made to make it easy to find chords that share a lot in common with the starting chord. The D0 column tells how many notes are in common, D1 how many are one semi-tone away, etc. The "score" is a measure of the "closeness" of the two chords, with the D0 score weighted more heavily than the D1, etc.
This was built using create-react-app and node-sass-chokidar.