Apache is a free and open-source cross-platform web server software.
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.
Polyfill is a service which accepts a request for a set of browser features and returns only the polyfills that are needed by the requesting browser.
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.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.