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.
m0n0wall is probably the first UNIX system that has its boot-time
configuration done with PHP, rather than the usual shell scripts,
and that has the entire system configuration stored in XML format.