Kamp: A Generation Lost in the Bazaar

It doesn't matter much that Mac OS X is POSIX compliant or certified, since POSIX and Unix(tm) don't standardize any user interface - or at least not any UI that a user-facing application would want to use. Libraries like Qt go a long way towards a cross-platform interface for writing applications, but there still remains a lot of work to port and maintain your program from Linux to Mac, or vice versa.