OpenBSD started as a fork of NetBSD. It is considered one of the most secure operating systems with the statement "Only one remote hole in the default install, in more than 8 years!" on their website. The OpenBSD team constintly audits the code for security problems and keeps a general level of parinoia.
The OpenBSD project has released several useful subprojects including 
OpenSSH, OpenBGDP, OpenNTPD and are working on OpenCVS.
OpenBSD has a ports system originally borrowed from FreeBSD but has now diverged.