nginx [engine x] is a HTTP server and mail proxy server written by me (Igor Sysoev).
nginx has been running for more than four years on many heavily loaded Russian sites including Rambler (RamblerMedia.com).
In March 2007 about 20% of all Russian virtual hosts were served or proxied by nginx.
According to Google Online Security Blog year ago nginx served or proxied about 4% of all Internet virtual hosts.