Linux	A UNIX-like operating system kernel built by volunteers. http://www.kernel.org
BSD	A variety of UNIX. See also: FreeBSD, OpenBSD, NetBSD
FreeBSD	A freely available BSD based operating system. http://www.freebsd.org
OpenBSD A freely available BSD based operating system with a focus on security. http://www.openbsd.org
NetBSD	A very portable, freely available BSD based operating system. http://www.netbsd.org

