  We present a new parallel PM N-body code named PMFAST that is freely
available to the public. PMFAST is based on a two-level mesh gravity solver
where the gravitational forces are separated into long and short range
components. The decomposition scheme minimizes communication costs and allows
tolerance for slow networks. The code approaches optimality in several
dimensions. The force computations are local and exploit highly optimized
vendor FFT libraries. It features minimal memory overhead, with the particle
positions and velocities being the main cost. The code features support for
distributed and shared memory parallelization through the use of MPI and
OpenMP, respectively.
  The current release version uses two grid levels on a slab decomposition,
with periodic boundary conditions for cosmological applications. Open boundary
conditions could be added with little computational overhead. We present timing
information and results from a recent cosmological production run of the code
using a 3712^3 mesh with 6.4 x 10^9 particles. PMFAST is cost-effective,
memory-efficient, and is publicly available.
