Music that uses tuning systems other than 12-tone equal temperament (12-TET) is often referred to as "microtonal". 12-TET arose as an approximation of Just Intonation so that it was possible to modulate to any key. However, it's not a very close approximation. Other tuning systems, often called "microtonal" systems, provide better approximations.

Many instances of this type of microtonality can be found on this site by searching the [tag:microtonality] tag. One in particular that might be of use:

* [Microtonal theorists who go beyond describing temperament and scale construction][1]


  [1]: https://music.stackexchange.com/q/75208/70803