Hping
- A network scanner that uses spoofed source address packets. Mainly used to test firewall rules and to perform advanced TCP/IP related attacks like the idle scan.
- http://www.hping.org/

Fake
- Allows the user to take over the IP address of another machine in the user's LAN via ARP spoofing.
- http://www.vergenet.net/linux/fake/

Razorback
- A log analysis program that interfaces with the SNORT open source Intrusion Detection System to provide real time visual notification when an intrusion signature has been detected on the network.
- http://www.intersectalliance.com/projects/RazorBack/

BitDefender Linux Edition v.7.0 (for Workstations)
- Free effective anti-virus security solution for systems running Linux; free updates of all signature files and high scanning speed.
- http://www.bitdefender.com/

Etherboot
- Free software package for booting x86 PCs over networks.
- http://etherboot.org/

COPS
- The famed Computer Oracle and Password System is a suite of tools that can automatically detect configuration problems or holes in your system.
- http://www.trouble.org/cops/

COLD
- Protocol LAN analyzer that can monitor various interfaces: ISDN, PPP, Token Ring, standard: loopback, 10baseT Ethernet.
- http://www.ipv4.it/cold/

Linux-PAM
- Linux Pluggable Authentication Modules (PAM) is a flexible mechanism for authenticating users using alternative authentication schemes.
- http://kernel.secsup.org/linux/libs/pam/

Stadrin
- Strong user authentication and access control for Linux environments in a fully integrated system using PAM modules.
- http://www.stadrin.com

IPTraf
- IPTraf is a console-based network statistics utility that gathers TCP connection paket and byte counts, interface statistics, and activity indicators. Also captures all TCP/UDP packets.
- http://iptraf.seul.org/

GNUPG- Gnu Privacy Guard
- An open source OpenPGP compatible encryption system. Provides data integrity services for messages and data files by using digital signatures, encryption, and compression.
- http://www.gnupg.org/

Central Command - Vexira Antivirus Solutions
- Vexira Antivirus for Linux workstations and servers. A complete virus defense system designed for easy and dependable virus prevention on Linux systems.
- http://www.centralcommand.com

IP Filter - TCP/IP Packet Filtering package
- An advanced TCP/IP packet filter suitable for use in firewall environments. Can be loaded as a module or compiled into the kernel.
- http://cheops.anu.edu.au/~avalon/ip-filter.html

JunkBuster
- Freeware for Unix/Linux/FreeBSD/OS2/BeOS/Windows 95/98/ME/NT4. Web proxy that filters banner ads, cookies, and referer tracking. Supports wafers and User-Agent spoofing.
- http://internet.junkbuster.com/

icmpquery
- icmpquery is a tool for sending and receiving ICMP queries for the destinations address mask and current time.
- http://www.angio.net/security/

Ethereal Network Analyzer
- Network protocol analyzer for Unix that allows examination of data from a live network, or from a capture file on disk.
- http://www.ethereal.com

EPAN - Ethernet Protocol Analyzer
- A protocol analyzer that supports ethernet, Token Ring, SLIP, PPP, ISDN, and loopback.
- http://www.et-inf.fho-emden.de/~tobias/epan/

DrawBridge
- A BSD-based firewall with source included. This binaries main value is that it is perfect for beginners learning how firewalls are developed.
- http://drawbridge.tamu.edu/

Cistron RADIUS Server
- An authentication and accounting server for terminal servers that speak the RADIUS protocol.
- http://www.radius.cistron.nl/

Deception Toolkit
- Performs emulation of other operating systems and vulnerabilities not found on the host; in order to deceive and solicit invaild attempts of exploitation by malicious individuals.
- http://all.net/dtk/download.html

DeleGate
- An application-level gateway server.
- http://www.delegate.org/delegate/

FreeTDS
- Free Tabular DataStream package. Tabular DataStream is a client-to-database server protocol in SyBase and Microsoft SQL database implementations.
- http://www.freetds.org/

Dante
- A circuit-level firewall and proxy that can be used to provide convenient and secure network connectivity to a wide range of hosts. Very similar to a SOCKS implementation.
- http://www.inet.no/dante/

CTC
- Freeware PGP, Pretty Good Privacy interoperable encryption software package. CTC is Rot13 for PGP.
- http://www.bifroest.demon.co.uk/ctc/

CIPE
- A Crypto IP Encapsulation project. Offers a protocol that passes encrypted packets between prearranged routers in the form of UDP packets.
- http://sites.inka.de/sites/bigred/devel/cipe.html

Arping
- A set of network diagnostic tools, such as an enhanced replacement for traceroute.
- ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz

Cheops
- Cheops is a complex network utility integration tool that offers network topographic visualization.
- http://www.marko.net/cheops/

ADMsmb
- A network scanner that detects Microsoft Windows shares using the SMB protocol.
- ftp://ADM.isp.at/ADM/ADMsmb-v0.2.tgz

ippl - IP Protocols Logger
- Performs logging of incoming IP packets by utilizing a multi-threaded approach. Administrators can perform filtering of captured packets.
- http://pltplp.net/ippl/

ipgrab
- A packet sniffing tool, based on the Berkeley packet capture library; that prints complete data-link, network, and transport layer header information for all packets it sees.
- http://ipgrab.sourceforge.net/

Mason
- Tool that interactively builds a firewall using ipfwadm, ipchains, or netfilter/iptables firewalling. [GPL]
- http://mason.stearns.org/