NARC (Netfilter Automatic Rules Configurator) is a free firewalling package for Netfilter/Iptables, released under the BSD license. It attempts to simplify the setup of a firewall (stateful packet filter) via the iptables tools. It is a bash shellscript that generates (hopefully) sensible and secure rules for Netfilter based on a simple configuration file. It features quick setup via a simple configuration file, connection tracking (and fragmentation reassembly), customized logging, probe detection (TCP & UDP), and much more.
FireHOL a simple yet powerful way to configure stateful iptables firewalls. It 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, and all kinds of NAT. It provides strong protection (flooding, spoofing, etc.), transparent caches, source MAC verification, blacklists, whitelists, and more. Its goal is to be completely abstracted and powerful but also easy to use, audit, and understand.
Frankenwall is a bash shell script intended to create a highly secure IPTables based Linux firewall/router with QOS/traffic shaping/bandwidth management. Be certain you know exactly what your network needs before using it. The primary focus of this project is security through an intimate understanding of your networking requirements. All configuration is done by editing text files.
Snowfence is a simple no-configuration-required Linux iptables firewall for the Sharp Zaurus. It limits the ability of potential attackers to access the Zaurus's services remotely while still allowing the Zaurus's legitimate local user to make use of the network and USB cradle as usual.
RWSecure parses the /var/log/secure (or specified secure log) file for invalid usernames or failed passwords. If more than a specified number of invalid or failed attempts are made by one IP, indicating a brute force attack, it will add that IP to your /etc/hosts.deny file by default.
IP-Array is a Linux iptables firewall script written in bash. It allows the creation of precise, stateful rules, while remaining easy to configure. IP-Array supports VPN, traffic shaping (creation of custom HTB and SFQ qdiscs, classes, and filters), multiple external interfaces, multiple LANs, multiple DMZs, NAT, logging, MAC address matching, packet marking, syslog logging, and various sysctl settings. It also includes some presets and autoconfig options for common needs like DNS, FTP, SMTP.