The app will make you play your lowest-proficiency songs (something you just started learning) daily. Medium-proficiency songs (you can play them, but you have room for improvement) get played several times a week. High-proficiency songs (you have mastered them) are cycled through at the rate of approximately one-two per day.

This app is in no way complete and probably contains bugs. With that being said, I have been daily-driving it in its current state for several days without problems.

There is no Apple version because I would have to buy a Mac and pay Apple $100/year for an iPhone app that I wouldn't even use.

Hopefully you find this helpful!