Advisory Check is a program that reads security advisories for you. It gathers security advisories using RSS, RDF, or XML feeds, compares them against the installed software, and alerts you if you're vulnerable. A wide variety of package managers can be queried to detect installed software. Remote systems can be monitored by using the integrated SSH, Windows-RPC, and Nmap support.
Spamresponder is a very simple and radical spam filter, combining DNS validation with the challenge/response approach. It will go through all mail messages in /var/mail/$USER, looking for specific "trusted" strings in the header and body parts of the mail. It will delete and send an automatic reply to messages which have no "trusted" strings inside them. Those replies will include one of the "trusted" strings, so the recipient just needs to reply to this confirmation message. The MailFrom-address of an email containing a trusted string becomes a trusted string itself.