cdnjs is a free distributed JS library delivery service.
Google Font API is a web service that supports open-source font files that can be used on your web designs.
Google Hosted Libraries is a stable, reliable, high-speed, globally available content distribution network for the most popular, open-source JavaScript libraries.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Three.js is a cross-browser JavaScript library and application programming interface used to create and display animated 3D computer graphics in a web browser using WebGL.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.