HardenedBSD is a security-enhanced fork of FreeBSD.
HardenedBSD aims to implement innovative exploit mitigation and security solutions for FreeBSD. Security is like an onion--it's made up of layers. In order to be successful, attackers must peel back each layer. HardenedBSD takes a holistic approach to security by hardening the system and implementing exploit mitigation technologies.
More information at http://hardenedbsd.org.