An excellent tool when you want to learn a new clef, whether it's for band, choir, music theory, or just your own hobby.
I originally designed this when I wanted to learn Tenor clef but couldn't find any good resources. Realizing that other people might have the same problem, I extended the code to fit other clefs. (With the new code setup, I replaced Tenor with Alto. I'm trying to figure out how to add it back.)
So far, the only clefs supported are Treble, Alto, and Bass. More clefs can be added at request or by dropping a pull request.