@Raphink It's a class that I'm developing. It's really for putting articles on the nLab, but since the main difficulty is getting TeX to produce something sensible as text then once I'd gotten a system for one then it wasn't hard to do the other. There's a slightly old version on my homepage at
math.ntnu.no/~stacey/HowDidIDoThat/LaTeX/internet.html but as I'm actively using it, I keep encountering new issues and don't update that page very often (at all!).