MPI
Point-to-Point communication
MPI_Send(mess, strlen(mess)+1, type, 1, tag, MPI_COM);
MPI_Recv(mess, leng, type,0, tag, MPI_COM, &status);
MPI_Bcast (inbuf, incnt, intype, root, comm);
MPI_Gather (outbuf, outcnt, outype, inbuf, incnt,..);
MPI_Reduce (inbuf, outbuf, count, type, op, root, ...)
As PVM, MPI offers a low-level programming model, but it id widely used for its portability.