BSD, yes

Apple's smart move (and I say that as someone who dislikes the company greatly - used to be an indi Apple Dev, so that sort of follows on naturally ;-) was to take a generously licenced, well tested, respected OS core and put all their effort into plugging the "Apple Experience" over it. The core OS is a commodity these days and this is how it likely should be done and everyone benefits - Apple (less core dev costs allowing them to focus on user experience) customers (better, lower cost OS) and even the BSD community somewhat (a high-profile implementation and Apple occasionally throws useful scraps of code back upstream).