Mac OS X
Mac OS X is a propietary, Unix-based operating system developed by Apple Inc. Based on BSD-Unix with a graphical user interface and API based on the dead OPENSTEP operating system from NeXT, it has become the most used and probably most popular Unix in the world. Its open source core, named Darwin, is based on FreeBSD 5.0 and the Mach 3.0 microkernel.
History
After the little success of Apple trying to create a modern operating system of its own, the company decided to use existing technology for the tenth version of its operating system. While Be Inc seemed to be the most appropiate candidate, NeXT's technologies were chosen as the basis for Apple's new operating system. Rhapsody, code name for the system, joined the Mach microkernel, a BSD operating system layer, the Yellow Box object-oriented frameworks from OPENSTEP and the Blue Box environment for backwards compatibility with the classic Mac OS. Rhapsody evolved into Mac OS X Server, which was the predecessor to Mac OS X.