How closely are Mac OS X and BSD related?

Question

I read that Mac OS X and bsd are related. How closely are they related. Can Mac OS X software be tweaked and installed on BSD?

Answer 1

If the Mac software uses Cocoa, Apple's proprietary display library (which it does, if it runs on the Mac with a GUI and does not require starting an X server), then you may have some issues running the code on a normal BSD system.

If your code only uses POSIX-specified functions, it will cleanly port to Linux, BSD, and even Windows.

It is true that Mac OS X and BSD are related. Although they have different kernels, they share a common ancestor and significant userland code. Obviously, I can't quantify "how close" - that's subjective.