nginx [engine x] is a HTTP server and mail proxy server written by
Igor Sysoev.
nginx has been running for more than three 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 nginx
serves or proxies about 4% of all Internet virtual hosts, although
Netcraft shows much less percent.
Here is one of the success stories:
FastMail.FM.