Major-thirds (M3) tunings are unconventional open tunings, in which the open strings form an augmented triad; in M3 tunings, the augmented fifth replaces the perfect fifth of the major triad of conventional open-tunings.
[1] Consequently M3 tunings are also called (open) augmented-fifth tunings (in French "La guitare #5, majeure quinte augmentée").
[2] Unfortunately, the open augmented-chord sounds dissonant to audiences who are accustomed to standard tuning.
[3] For a diatonic wind instrument (such as a harmonica or accordion), the blow notes repeat a sequence of (perhaps shifted to begin with E♭ or with G) and draw notes follow a repeating sequence of though perhaps with a different initial sequence.
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