Fityk [fi:tik] is a program for data processing and nonlinear curve fitting. It is primarily used by scientists who analyse data from powder diffraction, chromatography, photoluminescence and photoelectron spectroscopy, infrared and Raman spectroscopy, and other experimental techniques and also used to fit peaks – bell-shaped functions (Gaussian, Lorentzian, Voigt, Pearson VII, bifurcated Gaussian. EMG, Doniach-Sunjic, etc.), but it is suitable for fitting any curve to 2D (x,y) data. Fityk has the following features for users; intuitive graphical interface (and also command line interface), support for many data file formats, thanks to the xylib library, dozens of built-in functions and support for user-defined functions, equality constraints, fitting systematic errors of the x coordinate of points (for example instrumental zero error or sample displacement correction in powder diffraction). Manual, graphical placement of peaks and auto-placement using peak detection algorithm, various optimization methods (standard Marquardt least-squares algorithm, Genetic Algorithms, Nelder-Mead simplex), handling series of datasets, automation with macros (scripts) and embedded Lua for more complex scripting. The accuracy of nonlinear regression verified with reference datasets from NIST, an add-on for powder diffraction data (Pawley refinement), modular architecture, and an open source licence (GPLv2+).Subscribers have access to all versions of the program and to e-mail support. The program can be installed on many computers and can be also used after the end of subscription. Fityk is usually bought by companies and institutions. You may also like to read, Top Data preparation tools and platforms, Top Free Data Analysis Software, Top Data Mining Software , Top Free Data Mining Software, Data Ingestion Tools.