Apache HTTP Server is one of the most robust and fast cross-platform web servers. It´s been created from the open-source
idea showing once again that being associated to this idea is not a sign of failure and its backed up by being the most used web server in the world (from big and small business, to institutions and universities).
With Apache HTTP Server, we will be able to run CGI, Perl, Php3 + data bases, SSL, support for virtual host´s, IPv6 support, etc, basically nearly everything we ask from a web server.
Although it´s easy to install, it´s rather difficult in general to configure it before we start using it.