m0n0wall is an embedded
firewall distribution of
FreeBSD, one of the
BSD operating system descendants. It provides a small image which can be put on
Compact Flash cards as well as on
CD-ROMs and
hard disks. It runs on a number of embedded platforms and generic PCs. The PC version can be run with just a
Live CD and a
floppy disk to store configuration data, or on a single Compact Flash card (with an
IDE adapter). This eliminates the need for a hard drive, which reduces noise and heat levels.