Httpd server (Apache)
Apache is a free (open source) HTTP server software for Unix (BSD, GNU / Linux, etc.), Windows, Macintosh and other platforms, implementing the HTTP / 1.1 protocol  and the notion of virtual site. When it began its development in 1995 it was initially based on the popular NCSA HTTPd 1.3 code, but later it was completely rewritten. Its name is because Apache originally consisted only of a set of patches to be applied to the NCSA server. It was, in English, a patchy server (a patched server).
The Apache server is developed within the HTTP Server (httpd) project of the Apache Software Foundation.
Apache features among other features highly configurable error messages, authentication databases and content negotiation, but was criticized for the lack of a graphical interface that helps in its configuration.
Apache has wide acceptance in the network: in 2005, Apache is the most used HTTP server, being the HTTP server of 70% of the websites in the world and still growing its market share (historical statistics and daily use provided by Netcraft ).