Instruments by Harry Partch
The American composer Harry Partch (1901–1974) composed using scales of unequal intervals in just intonation, derived from the natural Harmonic series; these scales allowed for more tones of smaller intervals than in the standard Western tuning, which uses twelve equal intervals. The tonal system Partch used has 43 tones to the octave.
Source: Wikipedia — Instruments by Harry Partch (CC BY-SA 4.0)