Binaries of FitSuite are available freely for Linux and Windows alike. There are also newer versions (SnapShots) which were not checked thorougly, but which are used in our group. As stated in the License page the only provision is that you mention the program name (FitSuite), and properly cite the article on FitSuite (currently available at http://arxiv.org/abs/0907.2805v1} in your publication, for which you made use of FitSuite.
Sources of the main program will be provided on request. The sources of the algorithms used for simulation are already included in the binaries.
FitSuite is currently being developed under openSuse 11.1. We successfully compiled FitSuite under a few other distributions and even installed the binaries (compiled under Suse) of FitSuite under other distributions, but these matters have not been tested in details. We will do our best to provide binaries of other distributions on the ftp site.
Furthermore, if you are interested in, you are welcome to download EFFI written by Hartmut Spiering.