Netcat is a featured networking utility which reads and writes data across network connections, using the TCP/IP protocol. It is designed to be a reliable "back-end" tool that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
Ophcrack is a Windows password cracker based on a time-memory trade-off using rainbow tables. This is a new variant of Hellman's original trade-off, with better performance. It recovers 99.9% of alphanumeric passwords in seconds.
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, revealing password boxes and analyzing routing protocols.
Windows XP Service Pack 2 is the latest service pack for Windows XP -- Service Pack 2 (SP2) -- is all about security. It provides better protection against viruses, hackers and worms, and includes Windows Firewall, Pop-up Blocker for Internet Explorer and the new Windows Security Center.
John the Ripper is a fast password cracker, currently available for many flavors of Unix (eleven are officially supported, not counting different architectures), DOS, Win32, BeOS, and OpenVMS. Its primary purpose is to detect weak passwords. Besides several crypt(3) password hash types most commonly found on various Unix flavors, supported out of the box are Kerberos AFS and Windows NT, 2000, XP, 2003, LM hashes, plus several more with contributed patches.