OS X's commercial credentials recently got a major boost from the Open Group. Thanks to the efforts of Apple's OS boss Kevin Van Vechten and his team, Leopard has cleared all of the hurdles required to attain UNIX 03 certification. That places Apple in elite company. Only Sun, IBM and HP are certified, so OS X turns the Big Three into the Big Four.
Here's Apple's Open Group brand certificate, which entitles Apple to use the UNIX brand. I suggest printing this on high rag content paper, framing it and hanging it in your server room or your Mac-graced cubicle. There are UNIX pretenders, and there is the real thing. Mac users, realize that qualifying for UNIX is no small feat, especially for an open source, BSD-based OS. The Open Group standards, the PDFs for which are idiotically marked as free but blocked from PDF download unless you buy your way into a membership, are rooted in System V. Apple is to be commended.
The UNIX 03 specifications cover libraries, system calls, terminal interfaces, commands and utilities, internationalization and the C language. That's the whole enchilada for ISVs (independent software vendors) porting their server and non-GUI applications to OS X. UNIX ISVs ought to climb on board, because once Leopard ships in October I expect Xserve sales to take a leap. Software developers should also keep in mind that the Leopard client OS is the same as Apple's server, minus the quite exceptional administrative tools, and the installed base of four and eight-core Mac Pro desktop/workstations is even larger. MacBook Pro users are carrying 4 GB notebooks. If you're put off by Objective-C and Apple's proprietary UI frameworks--you needn't be, although I do wish that someone would give Apple's frameworks the Mono treatment--you've got OpenGL, SDL, X Window, Wine, Java SWT, Flash, DHTML with Apple's Canvas extension, and my old flame, curses. Microsoft's Silverlight is sweet as well, and it's picking up steam.
Wondering if you want in? You do. Imagine coding on Mac and porting by recompile to RISC big iron.