If it's not Apache it's NGINX (engine-x). Built in C, NGINX is one of the largest web servers in use today on the internet, serving common sites such as Facebook, Netflix, Dropbox, and many more. This server forms the second tier of a LEMP stack and is the part that allows the server to interact with the web. The current version of NGINX that is out and running is 1.5.8 (your current version can be checked after installation with the command below).