nginx [engine x] is an HTTP and reverse proxy server, as well as a mail proxy server, written by Igor Sysoev. For a long time, it has been running on many heavily loaded Russian sites including Yandex, Mail.Ru, VKontakte, and Rambler. According to Netcraft nginx served or proxied 18.16% busiest sites in May 2014. Here are some of the success stories: Netflix, Wordpress.com, FastMail.FM.
Nginx (pronounced "engine-x") is an open source reverse proxy server for HTTP, HTTPS, SMTP,POP3, and IMAP protocols, as well as a load balancer, HTTP cache, and a web server (origin server). The nginx project started with a strong focus on high concurrency, high performance and low memoryusage. It is licensed under the 2-clause BSD-like license and it runs on Linux, BSD variants, Mac OS X,Solaris, AIX, HP-UX, as well as on other *nix flavors. It also has a proof of concept port for Microsoft Windows.
...Nginx uses an asynchronous event-driven approach to handling requests, instead of the Apache HTTP Server model that defaults to a threaded orprocess-oriented approach, where the Event MPM is required for asynchronous processing. Nginx's modular event-driven architecture can provide more predictable performance under high loads.