Smoothwall Express appliance
A Free firewall that includes its own security-hardened GNU/Linux operating system and an easy-to-use web interface.
More informations on http://www.smoothwall.org/about/
WebUI can be accessed at https://GREEN_IP:441/ after installation. GREEN interface is used for the LAN, RED for the WAN connections. ORANGE and PURPLE can be used for DMZ.
RAM: 256 MB
Documentation for using the appliance is available on https://sourceforge.net/projects/smoothwall/files/SmoothWall%20Manuals/