Music theory
Helpful Books
Music Theory Companion
PG App Studio
MyMusicTheory - music theory
myrApps s.r.o.
Music Theory Helper
johgru apps
Theory of music
Kirill Sidorov
Tenuto Music Theory
Rirpadev
Math theory
Sangakoo
Set theory
Probability theory
Music Crab : Easy Music Theory
Éric Zorgniotti