Apple - Open Source
   The "open source" portions of Apple technologies, including Darwin, aka the core of Mac OS X.
   http://developer.apple.com/darwin/

High Performance Computing using Mac OS X
   Collection of open source tools for scientific computation: binaries, source, documentation and instructions for installing Fortran, MPI, OpenMP, Cactus, Globus and similar packages.
   http://hpc.sourceforge.net/