The fundamental services and primitives of the OS X kernel
are based on Mach 3.0. Apple has modified and extended
Mach to better meet OS X functional and performance goals.
It is correct to say some parts of OS-X/macOS are based on FreeBSD, but not to the point of making an unconditional assertion. As to user-land utilities, many are the same as found in a FreeBSD distribution.
A little more.. Apple hired Jordan K. Hubbard, the FreeBSD co-founder, back in 2001 to work in the Core OS Engineering Department. His role at that time was manager, BSD technology at Apple, overseeing the BSD Technology Base for Darwin, the UNIX-based core of Mac OS X.
I remember a very early release of Darwin, was interested at the time to see if it would eventually become a standalone product, but it never did. I assume there was a lack of corporate support, much like how Google is now trying to slowly close AOSP via removing core pieces like the dialer.
Regarding OS-X/macOS:
(source: https://developer.apple.com/library/archive/documentation/Da...)Some portions of the OS-X/macOS kernel are based on FreeBSD however:
(source: https://developer.apple.com/library/archive/documentation/Da...)As the above states:
It is correct to say some parts of OS-X/macOS are based on FreeBSD, but not to the point of making an unconditional assertion. As to user-land utilities, many are the same as found in a FreeBSD distribution.