FreeBSD is one of the most stable and secure server operating systems available today and has been proven to be an ultra-reliable platform. Most Open Source software packages are available on FreeBSD including Apache, Lighttpd, Perl, Python, MySQL, PostgreSQL, Ruby on Rails etc. FreeBSD is used for powering many established websites such as Yahoo!
We are using the latest FreeBSD Jails witch allow each jail to have multiple IP-addresses and full network control. The jail environment is (almost) indistinguishable from a real dedicated server. Each jail can have their own routing, firewalls, VPNs, etc in addition to their own files, processes, user and superuser accounts.