NGINX, pronounced Engine-X, if you don't know it, is an open-source Web and reverse proxy server and e-mail proxy server to boot. It's has been used for years on many popular Russian Web sites such as Yandex, Vkontakte, and Rambler. In recent years, it's been picked up by major Western sites including Facebook and Wordpress.com.
These Web sites, and millions of others, have moved to NGINX because it's very fast and uses few system resources. The company has claimed that NGINX can deliver 10 times the performance of the leading Web server on the same hardware. I'm not sure about that but I do know it's faster than Apache or IIS. NGINX manages this by being event-based. So, it doesn't spawn new processes or threads for each Web page request. That means that even as the Web server load increases, memory use remains low and predictable.
NGINX can also be used to improve performance because it can be used as a reverse proxy. In this load balancing mode, NGINX still looks like an ordinary Web server but at the data center, Web requests are being distributed among multiple back-end servers. The net result is that NGINX provides very fast and stable Web services with minimal hardware.
So it is that, according to Netcraft, of the over half-a-billion Web servers they track, while Apache and IIS gained users their overall market-share of active Web sites fell as NGNIX gained both market share this month and absolute growth with an addition of 6.9M hostnames. This gives NGINX an all-time high of 9.63% of all Web sites.
In terms of Active Sites, NGINX gained 1.9-million which put it ahead of ISS by a nose with second largest number of Active Sites, 22,221,514. IIS is now in third with 22,142,114.
It's not much of a lead, and in total sites, IIS is still well ahead, but since IIS has been losing market share since June 2010 and NGINX has been growing rapidly, I think it's safe to say that by mid-year, the big two Web servers will be Apache and NGINX with IIS slowly, but surely, falling behind.