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.
JSDelivr is a free public CDN for open-source projects. It can serve web files directly from the npm registry and GitHub repositories without any configuration.
KaTeX is a cross-browser JavaScript library that displays mathematical notation in web browsers.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
Unpkg is a content delivery network for everything on npm.