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.
Headroom.js is a JS widget that allows you to react to the user's scroll. The header slides out of view when scrolling down and slides back in when scrolling up.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
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.