AMaViS (A Mail Virus Scanner) scans e-mail attachments for viruses using third-party virus scanners available for UNIX environments. It resides on a UNIX (Linux) machine and looks through the attached files arriving via e-mail, generates reports when a virus is found and sets the delivery on hold.
Firewall is a set of scripts (firewall, fwup, and fwdown) that implement an ipchains firewall and various forms of network address and port translation. All you have to do is read the policy file and edit it to reflect your topology and filtering policy. It supports many different types of network topology (single host, traditional forwarding, masquerading, port forwarding, alias port forwarding and NAT), up to 10 untrusted interfaces each with their own policy, and over 50 network applications. It also supports centralised administration of multiple remote firewalls (meta-firewall).
Mason is a tool that interactively builds a firewall using Linux' ipfwadm or ipchains firewalling. You leave mason running on the firewall machine while you are making all the kinds of connections that you want the firewall to support (and want it to block). Mason gives you a list of firewall rules that exactly allow and block those connections. It can either build a firewall from scratch for you or supplement an existing firewall.
The Seattle Firewall is an ipchains firewall that supports IP masquerading and can be used on a standalone system, on a dedicated firewall system, or on a multi-use gateway/server. It supports VPN via IPIP tunnels, IPSec, and PPTP. It is easily configurable by editing configuration files, and can be extended without modifying the base product. It also includes realtime monitoring with an audible alarm that sounds when suspect packets are detected.
fwanalog is a shell script that parses and summarizes firewall logfiles. It understands logs from ipf (xBSD, Solaris), OpenBSD 3.x pf, Linux 2.2 ipchains, Linux 2.4 iptables, and a few types of routers and firewalls (Cisco, Checkpoint FW-1, and Watchguard). The excellent log analysis program Analog is used to create the reports.