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.
Gravatar is a service for providing globally unique avatars.
Open Graph is a protocol that is used to integrate any web page into the social graph.
ShareThis provides free engagement and growth tools (e.g., share buttons, follow buttons, and reaction buttons) for site owners.
Varnish is a reverse caching proxy.