BSD is derived from UNIX source code (that was once included with UNIX). Over time, BSD had its UNIX code replaced with open code. BSD's license allows fully proprietary derivatives that do not share source code. BSD in turn was used to create ULTRIX , FreeBSD, OpenBSD, NetBSD, BSDi, BSD/OS (BSD/386), Dragonfly BSD, 386BSD, FreeSBIE, MirOS BSD, DesktopBSD, PC-BSD, SunOS, Tru64, Darwin, ClosedBSD, PicoBSD, Anonym.OS, ekkoBSD, OliveBSD, Gentoo/*BSD, Debian GNU/*BSD, MidnightBSD, pfSense, Paxym-FreeBSD, NeXTstep, Rhapsody and Mac OS X.