Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components.
cdnjs is a free distributed JS library delivery service.
D3.js is a JavaScript library for producing dynamic, interactive data visualisations in web browsers.
Google Analytics is a free web analytics service that tracks and reports website traffic.
Heroku is a cloud platform as a service (PaaS) supporting several programming languages.
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.
Popper is a positioning engine, its purpose is to calculate the position of an element to make it possible to position it near a given reference element.