Race to Your Goal! December 2020 JLPT

By using a lot of userscripts, see a list (and guide) here:

(you’ll have to install a browser extension to load these scripts though, like Tampermonkey)

From a quick look, it looks like Heatmaps (the big calendar thing) and some SRS breakdown / leeches. Also, a dark theme (the dark background), not sure where that’s from.