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.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
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.