It's an interesting coincidence - just yesterday I learned about FSet while searching for something else and thought it's interesting. However, after arriving at https://common-lisp.net/project/fset/Site/Project.html and reading through the page I left it without installing.

For the very wrong reason, too: I just couldn't find the source code. Obviously, I didn't try very hard, but on the project page (which looks a bit too minimal, btw, some CSS wouldn't hurt) I didn't find a link to the repo. I think it would be great if you added it on top of the project page.