Gaussian's main advantage is the GUI! If you need a gaussian basis set code, nwchem exists! Orca is another one. If you need a plane wave code but don't want

Gaussian's main advantage is the GUI! If you need a gaussian basis set code, nwchem exists! Orca is another one. If you need a plane wave code but don't want to shell for VASP, Quantum Espresso is awesome, and easy to compile. Then there's CP2k, whose gaussian basis with planewave auxiliaries are pretty decent at molecular dynamics boxes. And to set up structures in a GUI, Avogadro is very useful for molecules. VESTA is great at crystals if you are willing to do a little math. And in Python, ASE and Pymatgen will do everything else that the GUI can't. Don't get me wrong, Gaussian is a fantastic program, and their developers deserve every penny - but there's no scientific reason you can't use free codes! IMO, the big limiter to open science in computational chemistry isn't the codes. It's the lack of computer power the average consumer has.