Firewall - no_enter (made with Lisp) very stable
Antivirus - Vscan2.0.1-beta is stable but still beta? http://sourceforge.net
Intrusion Detection - Tripwire <---Nice
Vulnerability Scanner - Secure_look.pl <--- http://CPAN.org
Port Scanning - NMap (there a GUI for it out)
Packet Sniffing - IPTraf for Linux, don't know any good ones that work on Windows
Encryption - MD5_GTK++
Spam Blocking - Never used one I use FreeBSD I havent seen 1 popup
Spyware / Adware Blocking or Removal -
Enumeration Tools - NetCat