I would like some classical molecular mechanics forcefield library or super-simple program which does not have any external dependences, so that I can plug it into my software without worry of "dependency hell". Also I would like to modify it, so I would prefer something with simple and compact source code. It should do just one thing - in summary it should follow unix philosophy
For example there is rdkit but it seems to be too ambitius (lot of functionality I don't need, lot of source code and dependencies to care about). Also many molecular editors like Avogadro and OpenBable have some molecular mechanics implemented ... but it would be much more convenient to have clean simple library than try to extract this functionality out of big software package.
I don't have much requirements on precision of force-field, but I would prefer something which is as general as possible (e.g. UFF) for all elements and exotic bonding topologies although organic chemistry is main target, not something specialized to e.g. proteins like GROMOS, AMBER, CHARM etc.