In 2001 the American Mathematical Monthly published a paper on the Pythagorean theorem in n dimensions. (Unless you've seen this before, it doesn't say what you might imagine.) This prompted me to write up some work I had done back in the late 1960's on the subject. In doing the original work, I made use of an n dimensional analog of vector cross product, which I thought was not a known thing. It certainly is known now (click here), though I don't know when it was first conceived. At any rate, my paper is not publishable, but may be of sufficient novelty to be of interest to someone out there.
Paper, pdf format.