Is the Mac OS kernel the same as the Linux kernel? What is the difference?
The macOS kernel is called Darwin, which is based off of FreeBSD. FreeBSD and Linux are both UNIX-like operating systems, however FreeBSD is more “Unixy” than Linux because the roots of BSD are in the original AT&T Unix. GNU/Linux on the other hand uses GNU components so they aren’t Unix, per se. Fun fact, GNU actually stands for “Gnu is not Unix”.
Another major difference in between Linux and BSD are the licensing. The GNU GPL License allows you to modify and redistribute the source code, however you should release the code back to open source. BSD Licence on the other hand allows you to modify and redistribute the code, but leaves the choice on the user whether to keep it closed source or open source. There is a saying in the Unix community that the BSD License is “so free that it allows you to make the code non-free”.
That is how Apple managed to use BSD code and get away with making it closed-source.
Link to Quora: