Apache

The Apache HTTP Server, commonly referred to as Apache (pronounced /əˈpætʃiː/), is web server software notable for playing a key role in the initial growth of the World Wide Web.[2] In 2009 it became the first web server software to surpass the 100 million web site milestone.[3] Apache was the first viable alternative to the Netscape Communications Corporation web server (currently known as Oracle iPlanet Web Server), and has since evolved to rival other Unix-based web servers in terms of functionality and performance. The majority of web servers using Apache run a Unix-like operating system.
From Wikipedia, the free encyclopedia - http://en.wikipedia.org/wiki/Apache_HTTP_Server