[TallGuyShort]

Open-source, for one, but that's more than just a philosophy in BSD. One of the key design considerations touted by BSD communities is that the kernel and userspace are distributed and built as one cohesive system for which you can get all the source / rebuild on your system. And that's done far more often than in Linux and other more mainstream OSs. But it's not a BSD kernel and what's distributed / used is very far removed from open-source Darwin and anything you could rebuild yourself. On the more subjective side of things, BSDs tend to value simplicity and correctness over new features. OpenBSD takes this to an extreme, but FreeBSD still takes it a lot further than Apple does.

But other than having more claim to the UNIX title than Linux and having some BSD userland, it's really not technically a BSD at all. I'll grant you it's arguably a distant descendant of BSD under the surface or in your shell.