[prewett]

Maybe I should know what this is about, but after reading the web page and the Github site, it's unclear to me if this is a set of fonts I download, or a useful set of font CSS settings, or a font renderer or what. What problem is this solving? Why does this work better than just using good quality fonts in the browser? The examples look great, I just don't know what I'm looking at.

[nielsbot]

I think these are fonts that are generally available on common OSes, so no webfonts needed, in order of preference/specificity. You often (for me, an amateur, anyway) don't know which list of fonts and fallbacks ("stack") to specify if you want a "industrial" font for example. This site has done that research for you.