cdnjs is a free distributed JS library delivery service.
jQuery CDN is a way to include jQuery in your website without actually downloading and keeping it your website's folder.
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.
RequireJS is a JavaScript library and file loader which manages the dependencies between JavaScript files and in modular programming.
Unpkg is a content delivery network for everything on npm.
Vue.js is an open-source model–view–viewmodel JavaScript framework for building user interfaces and single-page applications.