What are the best Android apps for learning and understanding music theory?

Music theory is a vast field that has developed over a long period of time and continues to evolve. There are many different varieties of music practiced throughout the world, and that makes things more complex. However, there are significant commonalities between different musical traditions that make theory learnable and practically useful across genres.

Wikipedia serves as a helpful reference for foundational knowledge when you are starting out.

I found an Android application called Music Theory Companion that gave me substantial help in understanding various scales, chord selections within specific scales, chord construction, and the Circle of Fifths and Fourths across different scales. The app also has an integrated metronome with precise timing, which lets you play chords alongside the beat — keeping theory connected to rhythm from the start.

I hope this helps other music enthusiasts on their theory journey.