Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
NitroPack creates optimised HTML cache for fast page loading experience.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Site Kit is a one-stop solution for WordPress users to use everything Google has to offer to make them successful on the web.
WP Engine is a website hosting provider.