Free and Open Source Network Firewalls
Endian delivers an open source UTM firewall which consists of stateful packet inspection, application layer proxy for protocols including HTTP, FTP, POP3, SMTP. The UTM firewall also supports anti-spam security, web content filtering and VPN functionality based on OpenSource VPN.
Moonwall provides a firewall based on FreeBSD and a combination of other software utilities.
pfSense is a free open source firewall and router.
Shorewall firewall is a tool designed to configure Netfilter.
Smoothwall Express is an open source firewall based on a hardened GNU/Linux OS.
Sophos firewalls (formally Astaro) are offered in appliance, software and virtual based platforms. Sophos is a well-regarded security vendor and provides complete UTM functionality within its Astaro range of firewall devices. Sophos offers a free version of its firewall where you can deploy the basic firewall in your environment for free. Modules can then be purchased if other features are required such as content filtering and VPN.
StillSecure delivers a software based firewall solution known as Cobia. Cobia can be installed on VMware as well. Cobia includes the ability to perform Routing, DHCP, DNS, Wireless, Firewall, VPN, Content Filtering, Reporting and more. Cobia can use modules provided by StillSecure or other third party organisations and developers. Cobia software comes as a public community license and a commercial use license. Via the StillSecure Community License, users can freely download and modify the source code.
Vyatta Core is an open source firewall offering IPv4 and IPv6 routing, intrusion prevention, stateful firewalling, IPSec and SSL OpenVPN and more. A commercial version is also available at http://www.vyatta.com/.
Zeroshell is a Linux based firewall. The firewall has some good functionality such as the ability to load balance internet connections, integrate with LDAP, captive portal for web login authentication and more.
Zorp is an application layer firewall based on the Python scripting language.