The Parallel Compositing library enables developers to write scalable 3D graphics applications. The library does sort-last compositing, and works on both clusters and SMP machines. The API aims to be the MPI of parallel compositing.
JCGrid is an easy-to-use tools for real-world grid-computing. It requires only to install Java Runtime and you can easy split your cpu-intensive task among several Workstations/PC/Mac/etc. It includes support for POVRay and MandelGrid as usage examples.