Google Analytics is a free web analytics service that tracks and reports website traffic.
Imgix is a visual media platform for managing, processing, rendering, optimising and delivering your existing images.
Leaflet is the open-source JavaScript library for mobile-friendly interactive maps.
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.
Unpkg is a content delivery network for everything on npm.