Circle of Fifths is a free Android app developed by Josh Liebe that helps users understand music theory behind the 12 keys of the chromatic scale. The app is designed to help users visualize the music notation of different scales, compose chord progressions/modulations, and mix in key.

The app features a color-coded relationship between the major, minor, and diminished keys, along with a key signature and triad for each key. It also includes a chord/arpeggio for each key that can be muted or unmuted. Additionally, users can lock the circle to the currently selected key and view a tappable legend indicating the degree of each key in the currently selected group.

Circle of Fifths offers several color schemes and a modern UI following material design guidelines. Overall, it is a great tool for musicians and music enthusiasts who want to learn more about music theory. Download Circle of Fifths today and start exploring the world of music theory in a fun and interactive way!