openmusictheory.github.io
Open Music Theory is an open-source, interactive online textbook for college-level music theory courses. It was built on resources authored by Kris Shaffer, Bryn Hughes, and Brian Moseley, edited by Shaffer and Robin Wharton, and published by Hybrid Pedagogy Publishing. It is intended to support active student engagement in the theory classroom and is designed for inverted or flipped courses.