This is the first app to play microtonal scales and use just intonation ratios. It comes with 30 scales by default and scales can be modified. It also allows users to create new original ones. Other cool tools for musicians included in this app are scale harmonization and finding scales that can be used over specific notes or chords. There’s a limited free version to try it out, and then the full version which is only $2.99. Check it out and have some fun!