Nyx code solves equations of compressible hydrodynamics on an adaptive grid hierarchy coupled with an N-body treatment of dark matter. The gasdynamics in Nyx uses a finite volume methodology on an adaptive set of 3-D Eulerian grids; dark matter is represented as discrete particles moving under the influence of gravity. Particles are evolved via a particle-mesh method, using Cloud-in-Cell deposition/interpolation scheme. Both baryonic and dark matter contribute to the gravitational field. In addition, Nyx currently includes physics needed to accurately model the intergalactic medium: in optically thin limit and assuming ionization equilibrium, the code calculates heating and cooling processes of the primordial-composition gas in an ionizing ultraviolet background radiation field. Additional physics capabilities are under development.
Nyx is parallelized with MPI + OpenMP, and has been run at parallel concurrency of up to 2,097,152 (on NERSC's Cori).
More information on Nyx can be found here: http://amrex-astro.github.io/Nyx/
If you prefer to run depreciated BoxLib-based version of the code, then you can use the boxlib branch (which will no longer be updated).