Eugene Volokh at the Volokh Conspiracy posts something very non-legal.
It's a challenging math question. I wish I could say that I had figured out the answer already, but I haven't. And, having seen the answer, I'm not sure I can try it without pushing my attempt towards the already-known result.
The problem is still very interesting, though it is deep in the realm of math-problems-without-an-obvious-real-world-use.