Mac marks the enterprise - Unix's power and flexibility combined with Apple's end-user savvy pose a true challenge to Windows and Linux.

IN MAY 2001, Apple began shipping OS X on new Macs. Six months later, at the O'Reilly Peer-to-Peer and Web Services conference, it was clear that a sea change was under way. The open-source geeks who flock to these events were flouting Microsoft not with PC notebooks running Linux, but with PowerBooks running OS X. Displayed on their gorgeous Aqua screens was the Mac's newest and most unlikely killer app: SSH, the secure shell, in all its 80-column, 25-line splendor.

Tim O'Reilly, founder and president of O'Reilly & Associates, is a technology trendspotter. He charts the course of his publishing business by watching the alpha geeks whose entry into various domains (the Internet, Linux, Wi-Fi) is a leading indicator of mainstream adoption. The trick, of course, is to separate signal from noise; the vision of a Unix-based computer with a friendly face is hardly new.

No less an alpha geek than Tim Berners-Lee endorsed that vision when he created the first Web browser on a NeXT cube. That legendary computer, introduced in 1988, had all the essential ingredients of the …