NeXTStep is a mix of BSD UNIXsoftware and the Mach kernel. It's not pure BSD UNIX, but from the end user point of view, that distinction is academic.

Call me crazy, but I don't consider middleware like iTunes to be a part of an operating system. I'll give you Cocoa and Carbon and all the frameworks that Apple bundles (really, does anyone consider WebKit to be a part of the OS?!), and I'll agree that Aqua is not CDE (ick, though the simplicity does have its charm at times) or even X based, but the GUI system is not what defines UNIX.

Did you know that you can run KDE on your OS X box? ssh into it and start KDE remotely. (Of course, you have to install it first.)

Check this out: http://finkcommander.sourceforge.net/ FinkCommander should scratch that free open source software itch...

Maybe this is also an academic question, but would you not consider Darwin to be a BSD-like UNIX?

Peace,

Drew