Here is a short list of links for learning music theory and other related skills.

Online textbooks and learning resources

• musictheory.net, lessons and exercises for theory and ear training.
• Music Theory for the 21st-Century Classroom, an open-access textbook by Robert Hutchinson.
• Music Theory for Musicians and Normal People, convenient one-page summaries written by Toby Rush, covering freshman and sophomore theory.
• Open Music Theory, an open-access online textbook
• teoria.com, lessons and exercises for theory and ear training.
• Hex Music Theory, YouTube videos, analyses, and supplemental materials for a wide variety of theoretical applications. From popular music to classical, guitar stuff, schema theory, Taneyev-style counterpoint, and more.
• Dave Conservatoire, a Khan Academy style website.

Books

• Christensen, Lars. The Cambridge History of Western Music Theory

Notation software

• Musescore

• flat.io

Other programs

• Audio Timeliner, analysis graphing software by Brent Yorgason.

Online Tools

• Juicio Brennan’s Lyric Hyphenator - Automatically hyphenates lyrics. Saves time when copy-pasting into notation programs.

• PC Set-Class Calculator - By David Walters at Mount Alison University.

• TrainedEar PC Set-Class Calculator - Another set calculator. Has links to more such tools.

• ToneSavvy - Exercises for many normal music theory things, but notable for its first species counterpoint trainer.

• Artusi: Counterpoint - A demo of the Artusi software, but it has some exercises in counterpoint up to fourth species with decent error detection.

• WesterParse - Westergaardian Species Counterpoint Online - Software based on the counterpoint rules of Peter Westergaard. Not as straightforward as the other counterpoint tools on this list, but certainly more flexible and robust.

YouTube channels

• Alan Belkin - classical composition and orchestration

• Bill Carmody - Music Theory chapter reviews of “Music in Theory and Practice” by Benward and Saker.

• David Newman - ear training and musicianship

• Dr. B / Christopher Brellochs - undergraduate theory and ear training

• Early Music Sources - counterpoint, Renaissance and Baroque music

• En blanc et noir - Partimento, classical improvisation

• GUIM - Schenkerian analysis of video game music (VGM)

• Jacob Gran - species counterpoint, Schenkerian analysis

• Jay Beard Music - atonal, set theory, Scriabin

• Jens Larsen - jazz guitar

• Kent Hewitt - jazz piano

• Metal Music Theory - self-explanatory

• Music Matters - ABRSM and undergaduate music theory, as well as various other topics

• NAETE - various pop and classical music topics

• Orchestration Online - orchestration

• The Prog School - progressive rock and metal composition

• Ryan Leach - composition, film and video game music (VGM), classical form

• Samuel Andreyev - 20th century composition and analysis

• Seth Monahan - undergraduate theory

• Signals Music Studio - pop and rock music, production

• Sideways - various topics, film music

• Things I Learned from Barry Harris - jazz guitar

• Walk That Bass - jazz piano

• 8-bit Music Theory - video game music (VGM)