X-Ray Crystallography software for Mac

*LTD* gave you some very good resources. Bill Scott's "Crystallography on OS X" pages have been around for quite awhile and offer a very thorough explanation of how to set things up on the Mac.

As noted by others, most of what you'll find is Unix-based and takes advantage of X11 windowing. Fink is also a useful package manager to assist with installing everything you need. It's really only been since Apple's switch to Intel in 2006 that it's been relatively easy to move these Unix apps onto the Mac, and more and more are making the transition.

My experience is with protein crystallography, and thus made extensive use of CCP4 and CNS for solution and things like Coot and PyMOL for modeling and visualization. I've used HKL on Unix plenty, and HKL-2000 works on OS X, but I don't have experience with how it runs there.

I don't have experience with small molecule crystallography, however, and there may be other good apps that I'm not familiar with that can handle direct methods phasing and other tasks for the smaller solutions.

There are a lot of apps out there and a lot of them are very specialized. It's probably a good idea to check with some of the people you're working with to see what they use for a given project. OS X is pretty popular with structure groups, and they frequently have resources in place to easily deliver what you need to your computer.