One of the other free UnixOperatingSystems.
FreeBsd (usually written as FreeBSD), along with NetBsd and OpenBsd are descended from the UNIX/"Unixy" systems developed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley (CalBerkeley) in conjunction with AT&T in the 1970s and 1980s. In the early 1990s, a lawsuit was settled that ended with the last of the "proprietary" source code being removed, and it's no longer "owned" by any company.
It used to be a server-centric OperatingSystem rather than a personal computer OS. But since its version 4, it has taken up the task of conquering Linux. DragonFlyBsd is a descendant/branch of the version 4 of FreeBsd. According to a poll that was conducted by the BsdCertificationGroup? in 2005, FreeBSD is the most popular BsdOs distribution.
They also call them packages since Ports can also mean different platform ports (NetBsd might even call their packages something else).
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FreeBSD is this operating system, which comes from BSD, which means that it is RealUnix. I like RealUnix, so therefore I like FreeBSD.