Open/Net/FreeBSD Unix IS unix. It's not just spawn, it's straight old-school Unix.
BSD was started when they got some code to the original AT&T Unix and created a academic version for their computers. Eventually they released a couple versions and they developed TCP/IP on them based on specifications dictated by the government's for Darpa. Since the BSD code was freely aviable many other commercial unix variants incorporated it's TCP/IP stack into their Unix systems.
This made Unix extremely desireable operating system family and eventually all the hundreds of commercial varations killed themselves off thru compitition Novell bought up the code and the copyright and eventually sued BSD saying that they didn't have a right to distribute commercial code originally obtained from AT&T. So thru several lawsuites Novell gave up and settled with BSD, and BSD rewrote the parts of the code that were determined to be original AT&T code. This whole ordeal is known as the Unix wars.
All of this nearly killed BSD and took it out as a major Unix player for a number of years.
During that time Linus created his own operating system kernel and combined it with majority of parts from the GNU Hurd operating system project to create "Linux/GNU" operating system.
Linux is not Unix. It has a completely different code base and different internal structure that was written apart from the BSD and System V (last realy popular commercial AT&T Unix) Unix variants.
BSD and System V share many common traits being based on the same original design, but have many differences. However the commercial System V variants have benifited heavily from incorporating BSD code into their operating systems over the years. And even Microsoft Windows NT has used and continues to incorporate BSD variants code into it's OS.
System V decendants still used today: AIX (IBM), Solaris (Sun), OpenSever (SCO), Unixware (SCO), HP-UX (HP). IRIX (SGI), True64 (HP) And a few others.
Out of those AIX, Unixware, and Solaris are still being actively developed. OpenServer is a very very common legacy operating system used in many small businesses and medium sized businesses. Although it's being erased by Linux's growth.
As a side note, Microsoft's first OS was Unix system V variant called Xenix. It was designed to run on i386 based hardware and back then Bill Gates said a few times that Unix was destined to be in every home. SCO in turn liscenced it to release SCO Xenix, and eventually bought the code completely from MS when MS abandoned it's Unix ambitions. Microsoft continued to use Xenix as it's internal operating system of choice upwards till Windows 3.11. Which is sorta ironic because DOS put MS on the map, but they did most of it's developement in Unix because DOS was unsuitable for most tasks.
BSD originally pretty much died off, and eventually NetBSD was created out of it. And out of that came a i386-specific version, FreeBSD... And eventually OpenBSD was created out of political friction from NetBSD.
Popular BSD Unix type OSes: Darwin (OS X), FreeBSD, OpenBSD, NetBSD among many other smaller variants.
Popular non-Unix unix operating systems: Linux, and the obsolete teaching tool: Minix.
Then there others like QNX were I am not sure were they fit.
Then there are Non-Windows Non-Unix-like OSes like BeOS, SkyOS, Netware, and quite a few others.
So it all depends on context on what your talking about.
Like you can say that 95% of desktops are Windows and 5% are Non-Windows-OSes.
Or you can say that sales numbers indicate all new installed server OSes, 50% are Windows, 25% are Linux, 20% are Commercial Unix, and the 5% are "other".
But if your going to ask "Does Non-Windows OSes support my laptop?" you will get answers ranging from "Yes, No, and Maybe" and probably all of them will be accurate.