Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
W3 Total Cache (W3TC) improves the SEO and increases website performance and reducing load times by leveraging features like content delivery network (CDN) integration and the latest best practices.
WPML plugin makes it possible to build and run fully multilingual WordPress sites.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.