A small price to pay
I completely disagree with the guy who complained that the app should be free. Yes, you can find all sorts of info on the web, but developing an app takes time and "free" is unreasonable given the effort to compile such useful and complex info in a way that makes it easy for anyone to understand.
Dont be fooled by the simplicity of this app. It includes advanced musical theories that I didnt see in a curriculum until the 3rd or 4th year. If it looks simple enough that reviewers can say "meh" speaks to to good work of the developers. Ill be using this to help illustrate musical concepts to my students.
Wasaga411 about
Theory Lessons, v2.4