cdnjs is a free distributed JS library delivery service.
Google Maps is a web mapping service. It offers satellite imagery, aerial photography, street maps, 360° interactive panoramic views of streets, real-time traffic conditions, and route planning for traveling by foot, car, bicycle and air, or public transportation.
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.
Typekit is an online service which offers a subscription library of fonts.