I just released Dover, a documentation coverage checking tool for Racket. If you make Racket packages, it will measure, with bar charts, how much of it you have or haven’t documented, and where the gaps are.
So, like most of my spare time coding Projects, it’s not something with broad application. However, if you have any interest in technical writing or programming languages, Racket’s remarkable documentation system (Scribble) is worth examining. When prose is itself code, you can do a lot of interesting things, particularly when the prose is also about code.