BSD

Berkeley Software Distribution (BSD, or Berkeley Unix) is an operating system based on Unix that was modified and distributed by the University of California, Berkeley. The term "BSD" can refer to its original system as developed at Berkeley, or by descendants including FreeBSD, NetBSD and OpenBSD.

Sun Microsystems made BSD popular in the 1980s as the operating system for its widely sold workstations.

BSD also refers to the BSD license agreement that allows free use and copying of source code, without the more stringent requirements of the GNU GPL. BSD is currently the most popular UNIX like operating system in terms of users, represented primarily by the 1,490,000 Mac OSX users worldwide.