Nginx [engine x] is an HTTP and reverse proxy server,
a mail proxy server, and a generic TCP/UDP proxy server,
originally written by Igor Sysoev.
For a long time, it has been running on many heavily loaded
Russian sites including Yandex, Mail.Ru, VK, and Rambler.
According to Netcraft, nginx served or proxied 22.23% busiest
sites in December 2021.
Here are some of the success stories:
Dropbox, Netflix, Wordpress.com, FastMail.FM.