Express is a web application framework for Node.js, released as free and open-source software under the MIT License. It is designed for building web applications and APIs.
Google Analytics is a free web analytics service that tracks and reports website traffic.
jQuery is a JavaScript library which is a free, open-source software designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.
Stripe offers online payment processing for internet businesses as well as fraud prevention, invoicing and subscription management.
Twitter is a 'microblogging' system that allows you to send and receive short posts called tweets.