Netfilter and iptables are building blocks of a framework inside the Linux 2.4.x and 2.6.x kernel that enables packet filtering, network addresses [and port] translation (NA[P]T) and other packet mangling. This enable use as a firewall and router.

ICSA certified Firewall-1. Operates on NT, Solaris, HP-UX, AIX, and RedHat Linux. Integrates with Check Point's VPN Gateway and RealSecure IDS products.

Developers of the XSentry firewall and Trustix Secure Linux. Security science and research.

ICSA certified SecureZone and Sidewinder firewalls and application gateways. Embedded VPN capability. Integrates with Strikeback IDS product.

A graphical interfaced Open Source firewall for Linux.

The Linux Embedded Appliance Firewall, an application based on iptables, with a number of optional modules including logging and intrusion detection.

Free Linux TCP/IP packet filter, suitable for use in a firewall environment. Presently incorporated in FreeBSD, OpenBSD and NetBSD.

Astaro supplies integrated perimeter security software solutions that include firewall, VPN, virus, surf and spam.

A Linux based security distribution with web based management, stateful packet inspection, proxies, anti-virus, anti-spam, content filtering and VPN.

A set of proxies to build a firewall. Provides information and software on building free firewall and security solutions.