Usually used to describe temperaments that are not equal.
American Festival of Microtonal Music
The AFMM produces and commissions works which use pitches and musical scales which are not organized in the standard twelve tone to the octave equally tempered way.
Dictionary of Microtonal Music Theory
Dictionary of common terms used in just tuning and equal temperament style tunings.
FreeNote Music: Microtonal Guitars & Recordings
Microtonal instruments, recordings and books.
Center for microtonal music. Promotes microtonal music in all its forms. In English and Dutch.
Julian Carrillo and the Thirteenth Sound
Mexican music creator of microtonal system called the 13th Sound.
Lucy Tuning is a microtonal music system derived from pi and the writings of John Harrison.
LucyTuning is a microtonal system derived from pi, and the writings of John 'Longitude' Harrison.
Classical Guitar music in 17-Tone Equal Temperament composed by Charles Loli.
R. L. Reid's Notes on Microtonal Composition
Sound files and an introduction to the 43 tone scale.