It's LaTeX, tikz, and pgfplots for the images. Complied with xelatex to pdf and pdf2svg to svg. The rest is custom HTML and CSS. We use the Hakyll static site generator.
[1]: http://mirrors.ctan.org/graphics/pgf/base/doc/pgfmanual.pdf [2]: http://mirrors.ctan.org/graphics/pgf/contrib/pgfplots/doc/pg...