A History of Apple's Operating Systems

Kernelthread.com:

Mac OS X is a unique operating system in that it represents a rather successful coming together of paradigms, ideologies, and technologies that have usually resisted each other in the past. It is a result of the trials and tribulations of Apple and NeXT, as well as their user and developer communities. Mac OS X is perhaps one of the best examples of how a capable system can result through the direct or indirect efforts of corporations, academic and research communities, the Open Source and Free Software movements, and even individuals.

Apple has been around since 1976, and many accounts of its history have been told. If the story of Apple as a company is fascinating, so is the "technical" story of Apple's operating systems.