Libfairydust is a small wrapper library intended for use with GPU clusters that 'hijacks' CUDA and OpenCL calls. It can be used to 're-route' calls to a certain GPU, so a process requesting GPU#0 might end up running on GPU#4 without knowing (or caring) about it. This works completely transparently and does not need any sort of 'cooperation' from the application, changes to code, or relinking.
Moscrack is a WPA cracker for use on clusters. It supports MOSIX, SSH, and RSH connectivity and works by reading a word list from STDIN or a file, breaking it into chunks, and passing those chunks off to separate processes that run in parallel. The parallel processes are then executed on different nodes in your cluster. All results are checked and recorded on your master node. Logging and error handling are taken care of. It is capable of running reliably for long periods of time, without the risk of losing data or having to restart. Moscrack uses aircrack-ng by default. Pyrit for WPA cracking and Dehasher for Unix password hashes are supported via plugins.