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.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Twitter is a 'microblogging' system that allows you to send and receive short posts called tweets.
Varnish is a reverse caching proxy.