In order to get accurate information about complex systems depending on a lot of parameters, frequently different experimental methods and/or different experimental conditions are used. The evaluation of these data sets is quite often a problem. The correct approach is the simultaneous fitting, which is rarely used, because only a very few programs are using it and even those cover usually a narrow field of physics. FitSuite was written to tackle this problem, by providing a general and extendable environment for simultaneous fitting and simulation. Currently it is used for M\"{o}ssbauer spectroscopy, grazing incidence neutron and (non)resonant X-ray reflectometry, but in principle other experimental methods can also be added.
