REEF3D is an open-source hydrodynamics framework. The software is efficiently parallelized, designed to run on a large number of processors. High-order spatial and temporal discretization schemes result in accurate and stable numerical behavior. The modular programming approach allows the framework to incorporate a range of different flow solvers which together represent all relevant length scales. With a focus on coastal, marine and hydraulic engineering flows, tailor-made multiphysics solvers are available for a range of relevant problems (e.g. sediment transport or floating body dynamics).