MPI-Povray consists of a patch to the Povray 3.1g raytracer that distributes work amongst a number of processing elements. Communication between the elements if acheived with MPI message passing.
This patch will probably need more work but seems to work OK. It'll need plenty of testing. So far I've built it under Linux (MPICH) and IRIX (MPT/MPI and MPICH). Other *IX platforms should be OK as long as you have some MPI implementation installed. Please give it a go and see how it works for you. I'd be particularly interested in how it behaves on larger Linux clusters...
I haven't given much consideration to optimisation yet. There's probably some rationalisation I could do in the message passing code.
Using 52 R10000 CPUS on 2 SGI Origin 2000s with MPICH I rendered the PovBench test image in 4 seconds.