Apple’s Xgrid system comes delivered with OSX and is a simple way of getting into Distributed Computing. Its simplicity allows users to be able to quickly turn on the Grid system and quickly get to submit jobs. However, a layer of complexity can exist if more is required. Such as greater security, advance job tracing, as well MPI integration using OpenMPI.
Xgrid is currently in its first revision.
Note: OSX Server is required to be able to run the Xgrid controller daemon. However, it is also possible to run it on a OSX Client as the controller binaries are also available there. That said, i have yet to find out how to configure the controller daemon on a OSX Client easily.