PLUMED is an open source library which allows you to calculate free energy in molecular systems. The application is compatible with many molecular dynamics engines. Plumed is a free software and is written in C++.
PLUMED is licensed under GNU General Public License and all you have to do is to cite the authors in your work.
If you want to make a donation write us at contact[at]plumed-code[dot]org.
A new version will be available soon so stay tuned!
Thank you for your interest!