A free data analysis program for Mossbauer spectroscopy was developed to solve commonly faced problems such as simultaneous fitting of multiple data sets, Maximum Entropy Method and a proper error estimation. The program is written in C++ using the Qt application framework and the Gnu Scientific Library. Moessfit makes use of multi-threading to reasonably apply the multi core CPU capacities of modern PC. The whole fit is specified in a text input file issued to simplify work flow for the user and provide a simple start in the Mossbauer data analysis for beginners. However, the possibility to define arbitrary parameter dependencies and distributions as well as relaxation spectra makes Moessfit interesting for advanced user as well.