Frettle is a free, open source app that shows every note, chord shape and scale on the neck of a guitar, bass, ukulele, mandolin, mandola or banjo, and on the keys of a piano.
It has no ads and works offline.
Pick a chord to see all the ways to play it up the neck, with the root and intervals marked and barres drawn in.
Pick a scale to see it across the whole fretboard, in hand-sized groups to step through, and see the chords that fit it.
Tap any note to hear it, or place notes on the neck to name the chord they make.
It covers 6 and 7-string guitar, 4 and 5-string bass, ukulele (high or low G), baritone ukulele, mandolin, mandola
and 5-string banjo, in standard tuning, Drop D, DADGAD, open G, double C and other alternate tunings, or custom ones saved by name, with or without a capo,
and the 88 keys of a piano.