An open soruce graph partitioning package
Version: 0.91PyMetis is a Python wrapper for the Metis graph partititioning software by George Karypis, Vipin Kumar and others. PyMetis includes version 5.0pre2 of Metis and will wrap it using the Boost Python wrapper generator library.
Operating System: Mac OS X
So far, it only wraps the most basic graph partitioning functionality (which is enough for my current use), but extending it in case you need more should be quite straightforward.
Using PyMetis to partition your meshes is really easy - essentially all you need to pass into PyMetis is an adjacency list for the graph and the number of parts you would like.
NOTE: PyMetis is licensed and provided under the terms of the MIT License.