Apache

Apache is a freely available Web server that is distributed under an Open Source license. Version 1.3 runs on most UNIX-based  operating systems (such as Linux, Solaris, Digital UNIX, and AIX), on other UNIX/POSIX-derived systems (such as Rhapsody, BeOS, and BS2000/OSD), on AmigaOS, and on Windows NT/95/98. According to the Netcraft (http://www.netcraft.com/) web server survey in September 1998, more than 50% of all Internet servers were running Apache. Although Windows-based systems with Web servers from Microsoft, Netscape, and other companies are probably gaining in terms of numbers, Apache is likely to remain popular in enterprises and server locations (such as universities) where UNIX-based systems are prevalent.

Apache complies with the newest level of the HyperText Transport Protocol, HTTP 1.1. Free support is provided through a bug reporting system and several USENET newsgroups. Several companies offer priced support.