Apache is a free and open-source cross-platform web server software.
cdnjs is a free distributed JS library delivery service.
Intersection Observer is a browser API that provides a way to observe the visibility and position of a DOM element relative to the containing root element or viewport.
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.
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.
PHP is a general-purpose scripting language used for web development.
Unpkg is a content delivery network for everything on npm.