The PVM patch for POV-Ray gives POV the ability to distribute a rendering across multiple heterogeneous systems. Using the PVM code, there is one master and many slave tasks. The master has the responsibility of dividing the image up into small blocks, which are assigned to the slaves. When the slaves have finished rendering the blocks, they are sent back to the master, which combines them to form the final image.
Lustre is fully GPL
Please note that the comments here about Lustre not being freely available are quite out-of-date. The most recent version of Lustre has been freely available for immediate download for the past 2 years, since the 1.4.0 release.