JavaScript libraries
Polyfill io 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

Analytics
Clarity is a free user behavior analytics tool that helps you understand how users are interacting with your website through session replays and heatmaps

Payment processors
Experience every payment in the world with one line of code

Tag managers
Google Tag Manager helps make website tag management simple with tools solutions that allow small businesses to deploy and edit tags all in one place

Authentication
Documentation for developers on how to log users into your app or website with Facebook Login

Payment processors
Stripe powers online and in person payment processing and financial solutions for businesses of all sizes Accept payments send payouts and automate financial processes with a suite of APIs and no code tools