There are many free DFT codes (see a list here https://en.wikipedia.org/wiki/List_of_quantum_chemistry_and_solid-state_physics_software). If you look to have a GUI interface for the DFT code then you can freely download BURAI (http://nisihara.wixsite.com/burai), which include a windows version of Quantum Espresso.
There are many program package for density functional theory (DFT) calculation. Gaussian program is user freindly package that are two linux and windows systems.