potfit is released under the GNU General Public Licence Version 2.
By downloading the source code you agree to the conditions of that license.
The latest version of potfit can be downloaded here:
Previous potfit releases can be found here.
You can download the current version via anonymous git access at https://github.com/potfit/potfit.
If you want to send us your changes, you can send it to the potfit mailing list or as a pull request on github.