De Raadt makes a rival open source operating system called OpenBSD. Unlike Linux, which is a clone of Unix, OpenBSD is based on an actual Unix variant called Berkeley Software Distribution. BSD powers two of the best operating systems in the world--Solaris from Sun Microsystems (nasdaq: SUNW - news - people ) and OS X from Apple Computer (nasdaq: AAPL - news - people ).
Actually, SunOS through 4.1.x and Solaris 1.x are BSD based. Solaris 2.x and onwards are AT&T Unix System V based.
Thanks for clarifying that.