BSD Router Projects
fdgw (NetBSD/i386 one floppy system)
fdgw is a single floppy version of NetBSD/i386 (currently tested only on i386 1.5 stable and 1.6 stable). It is available in the NetBSD package system at pkgsrc/sysutils/fdgw/ . This allows you to easily build an fdgw image from any netbsd-1-5/netbsd-1-6 branch source tree.
fdgw is a minimal operating system. It can convert an old machine without HDD into a small router or NAT system. It provides several models: natbox, adslrouter, riprouter(IPv4/v6 RIPv1/v2), bridge (available only on NetBSD 1.6), mcastrouter6(IPv6 multicast routing) and proxybox(application level gateway) et.al.
The easiest way to get started with fdgw would be to download a pre-made floppy image which can then be customized. Images are available from ftp.netbsd.org. See http://www.netbsd.org/Ports/i386/faq.html#onefloppy .
Micro OpenBSD (?)
one floppy openbsd
soekris (flashdist: embedded OpenBSD installer)
opensoekris (domain exists, but the web content not found ?)
PsygNAT free firewall and NAT router based on OpenBSD/i386.