|Do a Google search for Routerlinux 1.1 - this is a small, router-centric Linux distribution that uses a 2.4 kernel with DOC support and some ethernet (incl. tulip) drivers compiled in, busybox, iptables, ip masquerade, freeswan, and various other goodies, all in under 16 MB uncompressed. The entire image fits on the DiskOnChip. It's also very simple to install and configure: just burn the ISO image to CDR, boot with a CDROM drive installed (either on the on-board IDE header or with a bootable PCI or ISA card), and flash the image to DOC when prompted. Reboot, and you have a working minimal linux installation with Slackware-like init scripts. No hard disk needed.|
I have the unit working like a charm with a 4-port 10/100 card installed (Routerlinux only supports 2-homed red/green firewalling out-of-the box, but it should not be too difficult to modify the scripts to allow 3- or 4-homed firewalls). This is similar to Smoothwall, but much more compact and minimal - a really nice project.
I've just started playing with it, and some very useful things can be done with it, including VPNs.