Security:
Global Security Resource
Exploits, vulnerabilities, videos, papers, shellcode.
SecurityFocus is the most comprehensive and trusted source of security information on the Internet.
Free open-source software:
Privoxy is a web proxy with advanced filtering capabilities for protecting privacy.
SSL-Explorer is a fully-featured, web-based SSL VPN server.
The world's most popular network protocol analyzer.
Free open-source disk encryption software.
Enigmail is an extension to the mail client of Mozilla Thunderbird and Mozilla Seamonkey which allows users to access the authentication and encryption features provided by GnuPG.
GnuPG allows to encrypt and sign your data.
ClamWin Free Antivirus comes with an easy installer and open source code.