HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Polyfill is a service which accepts a request for a set of browser features and returns only the polyfills that are needed by the requesting browser.
Quicklink is a JS library which aims to be a drop-in solution for sites to prefetch links based on what is in the user's viewport.
Unpkg is a content delivery network for everything on npm.
Vercel is a cloud platform for static frontends and serverless functions.