NeXTSTEP was based on Mach/BSD from the early days so it isn't recent.
Yes, but Apple updated a lot of the OS X BSD with FreeBSD components. It's why many man pages say FreeBSD.
Question is, how much did they give back to it?
LLVM/Clang and Grand Central Dispatch comes to mind. The MAC framwork is also a shared effort, but I don't know who is doing the heavy lifting. It's something.
All the ones I listed are the ones where they are significant contributors.
The much larger set of where they are mostly users, like the BSD userland tools, curl, Python, Perl, Tcl, Ruby, and so forth, I omitted. There are just too many.