There are several other free single disk Linux routers available. Here is a list of some that I have found. Many people have put in much time and effort in developing this software.

www.linuxrouter.org

floppyfw

lrp.steinkuehler.net

lrp.ramhb.co.nz

lrp.gibbsoft.com

Coyote Linux

LEAF - Linux Embedded Appliance Firewall