http

In considering the ramifications of a slow denial of service attack against particular services, rather than flooding networks, a concept emerged that would allow a single machine to take down another machine's web server with minimal bandwidth and side effects on unrelated services and ports. The ideal situation for many denial of service attacks is where all other services remain intact but the webserver itself is completely inaccessible. Slowloris was born from this concept, and is therefore relatively very stealthy compared to most flooding tools.

nginx [engine x] is a HTTP server and mail proxy server written by 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, although Netcraft showed much less percent.
According to Netcraft in March 2008 nginx served or proxied 1 million virtual hosts. The growing in picture and colour!
According to Netcraft in December 2008 nginx served or proxied 3.5 millions virtual hosts. And now it is on 3rd place and ahead of lighttpd.
According to Netcraft in March 2009 nginx served or proxied 3.06% busiest sites.