MPICH
From Christoph's Personal Wiki
MPICH is a freely available, portable implementation of MPI, a standard for message-passing for distributed-memory applications used in parallel computing. MPICH is Free Software and is available for Linux. Moreover, MPICH is a developed program library.
The original implementation of MPICH is called MPICH1 and it implements the MPI-1.1 standard. As of 2006, the latest implementation is called MPICH2 and it implements the MPI-2.0 standard, but does not yet support data translations between different hardware architectures.
Usage
Note: In these examples, I will be using DOT as my parallel-process program.
mpiexec -n 2 dot.lin.mpich example.com -procs 2