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.
Tippy.js is the complete tooltip, popover, dropdown, and menu solution for the web, powered by Popper.