After a few years of trial, error, and usenet messages, I know just about all the LaTeX I really need. And my needs are modest. Most of my documents use the same template (
tufte-latex), with the same set of packages; occasionally I need to learn something new for a specific purpose, but in general I've got a nice stable skill set.
You can probably see where this is going: I'm starting to get bored and starting to feel stagnant. Since I have what I need, the question is: what do I want?
And that's my question. I want to expand my TeX skills, but without a real need directing me, I'm not sure where to start. Is there a package, TeX variant, or something that's worth learning just because it's cool?
(And yes, I know I can browse CTAN at my leisure. I'm asking you what corners of the LaTeX kingdom you particularly enjoy playing in.)