Moreover, Apple publishes most of the source code for OS X -- primarily the system software, commands, and utilities that reside below the presentation layer -- as the Darwin open source project. After a long delay, Apple recently made the source code for Darwin x86 available online. Apple took over stewardship of Darwin and a sister project called DarwinPorts, which is a repository of ready-to-compile open source applications validated for the Mac.

Intel-based Mac hardware is proprietary only insofar as its design makes it possible for OS X to tell the difference between a Mac and a non-Mac PC. Salient details of the Mac's design are public and thoroughly documented so that developers working in OS X or another x86 operating system can fully exploit the Mac's features. The Mac boots with the standards-based Extensible Firmware Interface instead of a closed, proprietary BIOS, but Apple includes EFI extensions that transparently support operating systems that don't yet work with EFI.

"Why invest in OS X when Vista is going to wipe it off the map?"

If imitation is the sincerest form of flattery, Steve Jobs is blushing. Apple Vice President Bertrand Serlet held the keynote audience at Apple's 2006 Worldwide Developer Conference in a state of disbelief with a presentation showing that Vista's design is rooted in OS X Tiger to a degree that even a die-hard Mac zealot would find incredible.

When Vista ships, Apple will be delivering all of its new Macs with OS X Leopard. And if you're hung up on Vista, the third-party Parallels Desktop will run it at blistering speed as a guest OS under OS X. There will be no vice versa in Vista's favor.