This is software for music theoretic programming in the Mathematica environment.
It contains several sub-packages that comprise symbolic representation of music scores and events, operations and transformations on musical objects, music data formats import/export, music notation and visualization, and generative composition.
The capabilities and design of the MusicTheory package are mostly orthogonal and to some extent incompatible with the built-in Music package by Wolfram Research. This is done because the Music package does not adequately address the representation of music-theoretic abstractions.