freebsd, firewall

m0n0wall is a project aimed at creating a complete, embedded firewall software package that, when used together with an embedded PC, provides all the important features of commercial firewall boxes (including ease of use) at a fraction of the price (free software).
m0n0wall is based on a bare-bones version of FreeBSD, along with a web server, PHP and a few other utilities. The entire system configuration is stored in one single XML text file to keep things transparent.

http://m0n0.ch/wall/