My wife is a professional trombonist who also teaches private lessons in a variety of brass instruments. Her beginner students are especially in need of repeated drills on fingering / positions on their instruments. There are several training programs out there, and while each has useful features, my wife wasn't completely happy with any of them. Since she is married to a programmer :-) she figured she could acquire a program that had exactly the features she has been looking for.
So I've been working on this, and doing it in Common Lisp. I've been spending the majority of my time on it especially recently as a final push to get the first version out. While this has taken time away from direct work on Graphic-Forms, it has given me the chance to use GF as an application developer. That's a perspective that every library developer should take periodically; I believe "dogfooding" is a popular phrase these days :-) And this fingering training program has served as a good testcase.
So, this has been a slight detour in my work, but it's a worthy cause and a lot of fun, too.