Just perfect fifths are the basis of Pythagorean tuning, and are employed together with other just intervals in just intonation.
It had a tuning with 58 pitches in the space of an octave for performing music in just intonation and was championed by John Farey, Sr., who also directed attention to instruments developed for similar purposes by David Loeschman and William Hawkes.
Jon Catler is an American composer and guitarist specially known for playing microtonal guitars like 31-tone equal tempered guitar, a 62-tone just intonation guitar, and a fretless neck.
Indian musicians learn relative pitch by singing intervals over a drone, which is also described by W. A. Mathieu using western just intonation terminology.
David B. Doty, (born 1950), American composer and authority on just intonation
Michel Geiss, :fr:Christian Braut and Philippe Monsire built the Semantic Daniélou, a 36-tone (out of 53 just intonation notes listed in the book "Sémantique Musicale" by Alain Daniélou) electronic instrument, on behalf of the author, using staggered square key button keyboards from two Cavagnolo Midy 20 master keyboards, where each parallel row of keys offers a transposition by one comma.
This note is often corrected to 16:9 on the natural horn in just intonation or Pythagorean tunings, but the pure seventh harmonic was used in pieces including Britten's Serenade for tenor, horn and strings.