Circle of 5ths is an Android app developed by Anton Zhvakin that is a must-have for any musician, whether a beginner or a professional. This app is an excellent educational and reference tool that helps users understand the relationship between major and minor parallel keys. Additionally, it can be used for modulation from one key to another.

The app features an intuitive interface that makes it easy to use and understand. Users can navigate through the circle of fifths and learn about each key's corresponding chords, scales, and notes. The app also provides helpful tips and tricks for using the circle of fifths to improve their music composition and performance.

Overall, Circle of 5ths is an excellent app for musicians who want to improve their understanding of music theory and composition. It's available for free on the Google Play Store, making it accessible to anyone who wants to learn more about music theory.