I think you (and me as well) want BSD. Now the problem with the popular BSDs is the package managers suck by comparison to most Linux distros.
The problem is FreeBSD doesn't keep up with modern hardware and you have to work very hard to get a laptop that works specifically with it.
Together they make up the current XNU hybrid kernel. You can look at most of the sources at opensource.apple.com
There's certainly lots of FreeBSD in OSX, but it's not like OSX is just FreeBSD with a sugar coated Apple UI.