cdnjs is a free distributed JS library delivery service.
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.
Leaflet is the open-source JavaScript library for mobile-friendly interactive maps.
PHP is a general-purpose scripting language used for web development.
Unpkg is a content delivery network for everything on npm.
W3.CSS is a CSS framework developed by the World Wide Web Consortium (W3C), the main international standards organisation for the World Wide Web.