|Xgrid is a proprietary program and distributed computing protocol developed by the Advanced Computation Group subdivision of Apple Inc that allows networked computers to contribute to a single task. It provides network administrators a method of creating a computing cluster, which allows them to exploit previously unused computational power for calculations that can be divided easily into smaller operations, such as Mandelbrot maps. The setup of an Xgrid cluster can be achieved at next to no cost, as Xgrid client is pre-installed on all computers running Mac OS X 10.4 to Mac OS X 10.7. The Xgrid client was not included in Mac OS X 10.8. The Xgrid controller, the job scheduler of the Xgrid operation, is also included within Mac OS X Server and as a free download from Apple. Apple has kept the command-line job control mechanism minimalist while providing an API to develop more sophisticated tools built around it. These computers, or nodes, execute the instructions provided by the controller and then return the results. The controller assembles the individual task results into the whole job results and returns them to the initiating computer. Apple modeled the design of Xgrid on the Zilla program, distributed with NeXT's OPENSTEP operating system application programming interface (API), which Apple owned the rights to. The company also opted to provide the client version of Mac OS X with only command-line functions and little flexibility, while giving the Mac OS X Server version of Xgrid a GUI control panel and a full set of features.