Jazz Fretboard Explorer — Guitar
Comping, walking and soloing all start from knowing the fretboard: select a pitch and each EADGBE position that sounds it appears.
An interactive map of this seat's fretboard in EADGBE: tap a note and it lights wherever it occurs, so 6 strings stop being 6 separate things to memorise.
Use it to find one chord tone in three places, or to see why a voicing you know in one key is the same grip a few frets along in another.
Every note a set of changes asks this seat for is already somewhere on this board; the changes pages only say which ones.