If you use my code (or try and fail to use my code) then please send an email to the address on my uni.lu page saying roughly what you used it for and how you got on.
The FRESHS (Flexible Rare Event Sampling Harness System) code is online here. This is a parallel execution toolkit to combine the SPRES and FFS sampling algorithms with the LAMMPS, Gromacs and ESPResSo simulation programs (or with your own self-written code).
Full text of the paper which gives an in-depth look at the SPRES algorithm is behind a paywall at J Chem Phys, however you will find an earlier version of the paper on arXiv.
For now there is no way to cite the FRESHS software package other than the names of the authors. This should change soon.
I have written a library implementing the techniques documented in this open access J Chem Theory Comput article as a plugin for AMBER. This will be included in the next release (AMBER14), however if you don't use AMBER or if you can't wait until 2014 then I am happy to email you the library on request as an open source module to plug into your own code.