GROMACS is a versatile package to perform molecular dynamics, i.e. simulate the Newtonian equations of motion for systems with hundreds to millions of particles.
It is primarily designed for biochemical molecules like proteins, lipids and nucleic acids that have a lot of complicated bonded interactions, but but thanks to its speed, many groups also use it for research on non-biological systems, e.g. polymers.
Speed is one of the key features that makes GROMACS particularly attractive. Thanks to the strong emphasis on bottom-up performance tuning: hand-tuned CPU SIMD kernels are available for most CPU architectures, CUDA-and OpenCL-based GPU acceleration together with efficient multi-threading and neutral-territory domain-decomposition with MPI SPMD parallelization is supported.