potfit is a free implementation of the force-matching algorithm to generate effective potentials from ab-initio reference data.
It was originally developed at the Institute for Theoretical and Applied Physics in Stuttgart.
For further information about the history and funding see About potfit - the ITAP Force-Matching Code.
potfit is available as open source software released under the GPL.
The latest version can be downloaded here.
If you need help, please contact the potfit mailing list.