This paper describes new software-called GRANFILM-for computing linear optical coefficients for surfaces and thin layers. The underlying theory relies on the treatment of the electromagnetic boundary conditions at the surface using the notions of integrated electromagnetic excess fields and surface susceptibilities. Any type of Fresnel quantities (reflection, transmission, absorption or ellipsometric coefficients) and dielectric coefficients (energy electron loss cross-section) can be computed by this software for various kinds of surface morphology: thin continuous films, island layers made of truncated spheres or spheroids, or rough surfaces. The only restriction on the morphology is that the thickness of the surface perturbed layer is much smaller than the optical wavelength. GRANFILM covers most of the material developed by Bedeaux and Vlieger in the recently published book 'Optical Properties of Surfaces' (Imperial College Press. London, 2001).