cdnjs is a free distributed JS library delivery service.
Fastly is a cloud computing services provider. Fastly's cloud platform provides a content delivery network, Internet security services, load balancing, and video & streaming services.
GitHub Pages is a static site hosting service.
Google AdSense is a program run by Google through which website publishers serve advertisements that are targeted to the site content and audience.
MathJax is a cross-browser JavaScript library that displays mathematical notation in web browsers, using MathML, LaTeX and ASCIIMathML markup.
Typekit is an online service which offers a subscription library of fonts.
Varnish is a reverse caching proxy.