Sanewall is a firewall builder for Linux that uses an elegant language abstracted to just the right level. This makes it powerful and easy to use, audit, and understand. It allows you to create very readable configurations even for complex stateful firewalls. Sanewall can be used for almost any purpose, including control of any number of internal/external/virtual interfaces, control of any combination of routed traffic, setting up DMZ routers and servers, all kinds of NAT, providing strong protection (flooding, spoofing, etc.), transparent caches, source MAC verification, blacklists, and whitelists. Newer versions abstract the differences between IPv4 and IPv6, allowing you to define a common set of rules for both, while permitting specific rules for each as you need. Sanewall is a fork of FireHOL and can make use of existing FireHOL configurations.
Dowse eases the configuration of network routing for a local area network, starting from the setup of ARP-level static entries of known peers, IP-level firewall, DHCP configuration, and local DNS cache, up to an application layer transparent proxy and optional gateways to anonymous networks such as Tor and I2P. It consists of a minimalistic script which can run on any GNU/Linux box and which, from a central configuration point, controls Ebtables, Iptables, and all the daemons needed for such operations: DnsMasq, Squid2, and Privoxy. It comes with a module system for contributed add-ons like DNSCrypt-proxy and HTTPS-everywhere.
RCPlive is a router live CD based on Debian 7 and the RCP100 routing suite. It is a flexible firewalling and routing platform, configured using a command line interface syntax similar to the one found in commercial routers. The software runs directly from a read-only CD or USB stick, and provides persistence by saving the configuration into a file placed on an existing disk partition.
VyOS is a Linux distribution for routers and firewalls which features a unified commandline interface and a single configuration file, with an API for extending it. It includes BGP, OSPF, and RIP routing protocols, policy-based routing, a DHCP and caching DNS server, a Web proxy, and more. It runs on x86 physical machines and a variety of hypervisors, including KVM, Xen, VMWare, and Hyper-V. VyOS is forked from Vyatta and based on VC6.6 source code.
The Collax Security Gateway is a Unified Threat Management (UTM) Solution for small- and medium-sized businesses. It includes an easy to configure stateful inspection firewall, email security features including anti-spam and anti-virus, Internet access control, Internet SSL interception, Internet networking optimization tools, Internet network fault tolerance, clientless VPN technology, and remote administration.