  Simulations inform all aspects of modern astrophysical research, ranging in
scale from 1D and 2D test problems that can run in seconds on an astronomer's
laptop all the way to large-scale 3D calculations that run on the largest
supercomputers, with a spectrum of data sizes and shapes filling the landscape
between these two extremes. I review the diversity of astrophysics simulation
data formats commonly in use by researchers, providing an overview of the most
common simulation techniques, including pure N-body dynamics, smoothed particle
hydrodynamics (SPH), adaptive mesh refinement (AMR), and unstructured meshes.
Additionally, I highlight methods for incorporating physical phenomena that are
important for astrophysics, including chemistry, magnetic fields, radiative
transport, and "subgrid" recipes for important physics that cannot be directly
resolved in a simulation. In addition to the numerical techniques, I also
discuss the communities that have developed around these simulation codes and
argue that increasing use and availability of open community codes has
dramatically lowered the barrier to entry for novice simulators.
