IYY said: OS X is based on FreeBSD, not Linux.
actually Mac OS X history is:
Despite its branding as simply "version 10" of the Mac OS, Mac OS X has a history that is almost completely independent of the earlier Mac OS releases. Mac OS X is based on the Mach kernel and the BSD implementation of Unix, which were incorporated into NEXTSTEP, the object-oriented operating system developed by Steve Jobs's NeXT company after he left Apple in 1985.[[1]]("http://en.wikipedia.org/wiki/Mac_os_x#_note-0") Meanwhile, during the years without Jobs at the helm, Apple attempted to create a "next-generation" operating system of its own (see Taligent and Copland) with little success. Eventually, NeXT's OS—called OPENSTEP at the time—was selected to form the basis for Apple's next OS, and Apple purchased NeXT outright[[2]]("http://en.wikipedia.org/wiki/Mac_os_x#_note-1"). Jobs was re-hired, and later returned to the leadership of the company, shepherding the transformation of the programmer-friendly OPENSTEP into a system that would be welcomed by Apple's primary market of home users and creative professionals, as a project known as Rhapsody. After some missteps which threatened the loyalty of independent developers to Mac OS, and changes of strategy to ease the transition from Mac OS 9 to the new system, Rhapsody evolved into Mac OS X. Mac OS X has evolved through its successive versions, away from a focus on backward compatibility and toward "digital lifestyle" applications such as the iLife suite, enhanced business applications (iWork), and integrated home entertainment (the Front Row media center).
http://en.wikipedia.org/wiki/Mac_os_x
And since it is some what similar to "other" OS's which include BSD, BeOS etc. I will move this thread to the "Other" OS thread.
ubuntu-geek said: Welcome to the new Other Linux Talk forum. This is the perfect place to discuss other linux distro's and related OS's.