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.
Actim allows you to send and retrieve files, and to call command line programs on a target machine via emails. The application can handle both synchronous and asynchronous requests with basic security features. It has both command line and graphical user interfaces. This can be useful if, for example, your home PC does not have any access to your office workstation which is behind the company firewall.
Aps is a small tool for analyzing network traffic. It prints out a great deal of information about the relevant protocols including TCP, UDP, ARP, and ICMP. It allows you to filter IP addresses, hardware addresses, ports, and specific protocols. It comes with a little GTK-GUI displaying packet counters for each protocol.
Alt+Connect manages dialup connections, allowing a group of networked machines to share a single Internet connection through their server. Custom client software lets users to start or stop their internet connection, and the server (connectd) ensures that the connection remains up only while someone's using it. Features include support for multiple ISPs and links (modems or ISDN channels), connection control lists, ability to record the time a user spends online and charge him for it, and the ability to enable and disable IP forwarding as a machine starts or stops using the Internet.
Arno's IPTABLES Firewall Script is a secure stateful firewall for both single and multi-homed machines. It supports NAT and SNAT, port forwarding, ADSL ethernet modems with both static and dynamically assigned IPs, MAC address filtering, stealth port scan detection, DMZ support, protection against SYN/ICMP flooding, experimental IPv6 support, multi-interface/aliased-IP support, and extensive user definable logging with rate limiting to prevent log flooding. It has plugin support to add extra features (like SSH Brute Force protection and (Racoon) IPSEC support). It is easy to configure and highly customizable. A filter script that makes your firewall log more readable is also included.