Fityk [fi:tik] is a program for data processing and nonlinear curve fitting.

Primarily used:

• by scientists who analyse data from powder diffraction, chromatography, photoluminescence and photoelectron spectroscopy, infrared and Raman spectroscopy, and other experimental techniques,
• 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.