MPICH is an implementation of the Message-Passing Interface (MPI) standard.

The goal of MPICH is to provide an MPI implementation that supports
different computation and communication platforms including commodity
clusters, high-speed networks and proprietary high-end computing systems.
It also enables cutting-edge research in MPI through an easy-to-extend
modular framework for other derived implementations.

WWW: http://www.mpich.org/