The General Atomic and Molecular Electronic Structure System (GAMESS) is a general ab initio quantum chemistry package. Briefly, GAMESS can compute wavefunctions ranging from RHF, ROHF, UHF, GVB, and MCSCF, with CI and MP2 energy corrections available for some of these. Analytic gradients are available for these SCF functions, for automatic geometry optimization, transition state searches, or reaction path following.

GAMESS-UK is a general purpose ab initio molecular electronic structure program for performing SCF-, DFT- and MCSCF-gradient calculations, together with a variety of techniques for post Hartree Fock calculations. The program is derived from the original GAMESS code, obtained from Michel Dupuis in 1981, and has been extensively modified and enhanced sincce then. Available for free to U.K. academics.

GAMGI (General Atomistic Modelling Graphic Interface) is an object-oriented program aiming to handle all aspects directly related with building, viewing and analysing atomic strucures, such as molecules, crystals, glasses, liquids, etc.

GAMMA is a C++ library written for simulation of Magnetic Resonance experiments. Its purpose is to provide a simple and intuitive means with which users may construct simulation programs to suit their individual needs. A Python wrapper is also available.

Garlic is a free molecular visualization program written for both educational and professional research purposes.

Gaussian is an ab initio electronic structure program. Designed to model a broad range of molecular systems under a variety of conditions, it performs its computations starting from the basic laws of QM.

GaussSum is a GUI application that can analyse the output of Gaussian 98/03, ADF, GAMESS (US), GAMESS (UK), and PC-GAMESS calculations to extract and calculate useful information. This includes the progress of the SCF cycles, geometry optimisation, UV-Vis/IR/Raman spectra, MO levels, MO contributions and more.

GChemPaint is a 2D chemical structures editor for the Gnome-2 desktop. GChemPaint is a multi document application and is a bonobo server so that chemistry can be embedded in other Gnome applications.

GDIS (GTK Display Interface for Structures) is a visualization program for small molecules, crystals, and solution cells. It has support for common crystallographic file formats, and assorted tools for visualization (including diffraction pattern generation), manipulation, and model creation. Rendering of molecules and energy minimization are also possible via Povray and GULP.

gdpc is a program for visualising MD simulations. It is a very versatile program and could easily be used for other purposes. gdpc reads xyz input and custom formats and can write out pictures of the frames.