Comment by khitchdee

FWIW, A sitar also has a 12 note scale, but the frets are moveable so you can tune by ear. The drawback is, you only play melodies on the top string and there are no chords. It's possible to design a guitar where the frets are spaced at harmonic intervals and not equal tempered, but then, you can only play in one key, the key of E and you can't capo or play barre chords. However, if you do play such a redesigned guitar in the key of E, it will sound sweeter because all your notes will be harmonic and you could play chords.