In March 2001, Apple Computer released Mac OS X. By providing features such as protected memory and preemptive multitasking, which Windows users have long enjoyed, this UNIX-based OS became Apple's first viable alternative to the Windows 2000 line. A beautiful, liquid-inspired UI, dubbed Aqua, accompanies the technical improvements.

Mac OS X began life as NeXTSTEP, a gray-scale OS built on top of Steve Jobs's ill-fated NeXT Cube. NeXTSTEP eventually morphed into the OpenStep environment, which ran on a variety of platforms, including Windows NT. When Apple bought NeXT in late 1996, Apple worked to resurrect OpenStep into a new product, code-named Rhapsody. But Apple eventually deemed Rhapsody untenable and reconfigured the system yet again. Two years ago, Apple separated a server version, based largely on Rhapsody code, from the mainstream desktop version and released Mac OS Server.

The mainstream desktop version became known as Mac OS X. Early in the development of Mac OS X, Apple decided to take a three-way strategy—support current Macintosh applications, support the new Mac OS X environment, and provide a middle ground, called Carbon. Carbon is the API set that lets developers easily upgrade classic applications to provide all the benefits of Mac OS X.

Despite the OS's rock-solid underpinnings and beautiful UI, Mac OS X's arrival was surrounded by controversy. Early on, Apple decided to abandon OpenStep's crossplatform nature and made Mac OS X a Mac-only OS. In addition, Apple shipped the first release of Mac OS X without a few key features. Apple says it will rectify these shortcomings in time.

Apple also has other problems to deal with, including the success of open-source solutions such as Linux, which by most estimates has already surpassed the Mac user base. Apple says it has incorporated open-source code into Mac OS X, but because Apple's license is very restrictive, many open-source luminaries deride this claim as a publicity stunt. Mac OS X is largely a closed, proprietary system that runs only on the PowerPC platform, which has lost significant ground to Intel over the years.