Does anyone know of any good cpu clustering software that will allow me to build a supercomputer out of any number of commodity computers?

I looked at beowulf/openmosix a while back but I think the project is abandoned or something, I read it had architectural problems and it still used the older 2.4 kernel as well. I think MPI has replaced it as the right architecture but I'm not familiar with any actual implementations that are complete that I can just install, set up and run to get distributed computing power?

If anyone can recommend any suitable cluster server software I'd be grateful.