DSniff

"dsniff is a collection of tools for network auditing and penetration testing. dsniff, filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network for interesting data (passwords, e-mail, files, etc.). arpspoof, dnsspoof, and macof facilitate the interception of network traffic normally unavailable to an attacker (e.g, due to layer-2 switching). sshmitm and webmitm implement active monkey-in-the-middle attacks against redirected SSH and HTTPS sessions by exploiting weak bindings in ad-hoc PKI." read more...

Website: http://www.monkey.org/~dugsong/dsniff/

Cain and Abel

"Cain & Abel is a password recovery tool for Microsoft Operating Systems. It allows easy recovery of various kind of passwords by sniffing the network, cracking encrypted passwords using Dictionary, Brute-Force and Cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords, recovering wireless network keys, revealing password boxes, uncovering cached passwords and analyzing routing protocols. The program does not exploit any software vulnerabilities or bugs that could not be fixed with little effort. It covers some security aspects/weakness present in protocol's standards, authentication methods and caching mechanisms; its main purpose is the simplified recovery of passwords and credentials from various sources, however it also ships some "non standard" utilities for Microsoft Windows users." read more...

Website: http://www.oxid.it/cain.html

Memoryze

"MANDIANT Memoryze is free memory forensic software that helps incident responders find evil in live memory. Memoryze can acquire and/or analyze memory images, and on live systems can include the paging file in its analysis." read more...

Download: http://fred.mandiant.com/MemoryzeSetup.msi

snmpcheck

"snmpcheck is a free open source utility to get information via SNMP protocols. It works fine against Windows, Linux, Cisco, HP-UX, SunOS systems and any devices with SNMP protocol support. It could be useful for penetration testing or systems monitoring. snmpcheck has been tested on GNU/Linux, *BSD, Windows systems and Cygwin. snmpcheck is distributed under GPL license and based on Athena-2k script by jshaw. " read more...

Website: http://www.nothink.org/perl/snmpcheck

Winpooch

"Winpooch is a Windows watchdog, free and open source. Anti spyware and anti trojan, it gives a full protection against local or external attacks by scanning the activity of programs in real time. Associated with ClamWin antivirus, Winpooch keeps safe your computer against virus." read more...

Download: http://sourceforge.net/project/showfiles.php?group_id=122629

SpamAssassin: An Open Source E-mail Filter

"No list of open-source security tools would be complete without SpamAssassin. A two-time Datamation Product of the Year winner, this anti-spam tool is the "secret sauce" behind a number of commercial products, as well as being put to good use by a number of e-mail hosting vendors and spam filtering vendors. Experts often recognize SpamAssassin as the best open-source anti-spam tool available." read more...

Website: http://spamassassin.apache.org

OTPW: A One-time Password Login Package

"The OTPW package consists of the one-time-password generator otpw-gen plus two verification routines otpw_prepare() and otpw_verify() that can easily be added to programs such as login or ftpd on POSIX systems. For platforms that support the Pluggable Authentication Method (PAM) interface, a suitable wrapper is included as well. Login software extended this way will allow reasonably secure user authentication over insecure network lines. The user carries a password list on paper. The scheme is designed to be robust against theft of the paper list and race-for-the-last-letter attacks. Cryptographic hash values of the one-time passwords are stored for verification in the user’s home directory." read more...

Website: http://www.cl.cam.ac.uk/~mgk25/otpw.html

msramdmp: McGrew Security RAM Dumper

"Creating bootable USB drives for capturing the contents of memory: A short while back, a paper was published by researchers at Princeton University, in which they talk about the process of recovering encryption keys out of memory after a cold boot. This was surprising to many people, as most just assume that, since RAM is volatile storage, it is erased when power is removed. This is an incorrect assumption." read more...

Website: http://mcgrewsecurity.com/projects/msramdmp

Clam AntiVirus

"Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail gateways. It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. The core of the package is an anti-virus engine available in a form of shared library." read more...

Website: http://www.clamav.net

Sysinternals utilities

"One of my favorite set of free developer utilities on Windows is the sysinternals.com collection. Whether it's filemon to see what's writing to a file, regmon for the registry or process explorer to see what DLLs are in action (and much more), I find myself reaching for one or more utilities several times a year. Of course Microsoft bought the site a couple of years ago and the domain now redirects into Microsoft's site which thankfully is a bit quicker than it used to be." read more...

Website: http://sysinternals.com