Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
Open Graph is a protocol that is used to integrate any web page into the social graph.
SPIP is a content management system written in PHP that uses one or more databases like SQL, SQLite or PostgreSQL.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.