List_of_router_or_firewall_distributions
pfSense is a free, open source customized distribution of FreeBSD tailored for use as a firewall and router.
http://www.pfsense.org/
OpenSource forks of pfSense:
http://opnsense.org/
https://virtualpf.com/
http://m0n0.ch/
IPFire is a hardened Linux appliance distribution designed for use as a firewall.
http://www.ipfire.org/
http://www.endian.com/community/overview/
Endian Firewall Community (EFW) is a turn-key Linux based security software product designed for home that can transform any unused hardware appliance into a full-featured Unified Threat Management (UTM) solution. Endian Community is designed to make security simple and help protect home networks by using the power of Open Source.
http://www.zeroshell.org/