  We describe a major update to the public GIZMO code. GIZMO has been used in
simulations of cosmology; galaxy and star formation and evolution; black hole
accretion and feedback; proto-stellar disk dynamics and planet formation; fluid
dynamics and plasma physics; dust-gas dynamics; giant impacts and solid-body
interactions; collisionless gravitational dynamics; and more. This release of
the public code supports: hydrodynamics (using various mesh-free finite-volume
Godunov methods or SPH), ideal and non-ideal MHD, anisotropic conduction and
viscosity, radiative cooling and chemistry, star and black hole formation and
feedback, sink particles, dust-gas (aero)-dynamics (with or without magnetic
fields), elastic/plastic dynamics, arbitrary (gas, stellar, degenerate,
solid/liquid material) equations of state, passive scalar/turbulent diffusion,
large-eddy and shearing boxes, self-gravity with fully-adaptive force
softenings, arbitrary cosmological expansion, and on-the-fly group-finding. It
is massively-parallel with hybrid MPI+OpenMP scaling verified up to >1 million
threads. The code is extensively documented, with test problems and tutorials
provided for these different physics modules.
