The official release of GROMACS 2016 is now available.
What new things can you expect? Please see the release notes highlights at http://manual.gromacs.org/documentation/2016/ReleaseNotes/index.html#highlights.
All the content of GROMACS 5.1.3 (and subsequent bug fixes) is present (apart from features that have been removed).
You can find the code, manual, release notes, installation instructions and test suite at the links below.
Documentation: http://manual.gromacs.org/documentation/2016/index.html (includes install guide, user guide, reference manual)