Deception Toolkit - Make your system seem to have network security bugs, and log attack attempts..
FakeBo - Fakes trojan servers (Back Orifice, NetBus) and logs every attempt from client..
Flawfinder - Examines source code looking for security weaknesses..
Guarded Memory Move (GMM) - The GMM library can be used to prevent and study buffer overflows exploits.
Libsafe - Free software (GNU license) from Bell Labs for protecting internet servers from buffer overflow attacks, one of the most commonly exploited security vulnerabilities..
Samhain - A tool for file integrity checking that optionally can be used as a client/server application for centralized monitoring of networked hosts..