The Open Forcefield Toolkit provides implementations of the SMIRNOFF format, parameterization engine, and other tools. Documentation available at http://open-forcefield-toolkit.readthedocs.io
I read through the FAQ and am tagging some sections as slightly or significantly out of date. I don't have the time to work on these now, so I'm noting them for future changes.
"Can I use an AMBER (or GROMACS) topology/coordinate file as a starting point for applying a SMIRNOFF force field?"
This is no longer entirely impossible
"What about starting from a PDB file?"
Missing discussion of recent capabilities of loading some PDB files
I read through the FAQ and am tagging some sections as slightly or significantly out of date. I don't have the time to work on these now, so I'm noting them for future changes.