IPCop happens to be a Linux distribution with the sole function of acting as a hardware firewall, thus protecting your network from threats outside and from within. Speaking of support, I should also point out that IPCop has a number of very cool add-ons as well. My two favorites are Banish and Copfilter, which is used to filter out malware and viruses in real time.
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.
pfSense is a free, open source customized distribution of FreeBSD tailored for use as a firewall and router. In addition to being a powerful, flexible firewalling and routing platform, it includes a long list of related features and a package system allowing further expandability without adding bloat and potential security vulnerabilities to the base distribution.
The SmoothWall GPL project was founded in the summer of 2000 by Lawrence Manning (Principle Code Author) and Richard Morrell (Project Manager). Their goal was to create a Linux distribution that could convert a redundant PC into a hardened internet firewall device.
The Vyatta Community Edition (VC) is award-winning, Linux-based, open source software providing routing, firewalling, VPN, intrusion prevention, and WAN load balancing services, among others, for your network. When you run Vyatta on a standard x86 hardware system, you'll create a powerful network appliance that can run circles around proprietary systems.