cdnjs is a free distributed JS library delivery service.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Optimizely is an experimentation platform that helps developers build and run A/B tests on websites.
Typekit is an online service which offers a subscription library of fonts.
Zendesk is a cloud-based help desk management solution offering customizable tools to build customer service portal, knowledge base and online communities.