NeqSim uses the non-linear Levenberg-Marquardt parameter-fitting model. Examples in the GUI show you how to do parameter fitting to experimental data. A database with collected (and public) experimental data is distributed with the program (NeqSim Access database) – you will have to register it on your machine (ODBC-registry) to make it work.
NeqSim supports Monte-Carlo Simulations for predicting errors in fitted parameters.