ADF, the Amsterdam Density Functional program for the treatment of complex chemical problems.

A program for molecular orbital analysis. It calculates the MO compositions of the constituent chemical fragments from the output files of various quantum-chemical packages, analyzes chemical bonding using overlap populations, and generates density-of-states spectra. License required.

A free molecular modeling program for Windows9x operating systems with 3D-builder, various ab initio calculation modules and simple molecular mechanics.

Windows program for analyzing and visualizing molecules using the theory of Richard Bader. Demo version available.

Site critical of Gaussian, Inc.'s licensing practices. Reports allegations of Gaussian banning "competitors" from using their product.

Simulates complex chemical kinetics in reacting flow.

Commercial conformational searching and analysis tools for Linux, Mac OS X, and Windows. Compatible w/CAChe, ChemOffice, and Amber. Screen shots, data sheet, ordering, and trial versions available.

Unix program to compute the electronic structure of periodic systems within Hartree Fock, density functional or various hybrid approximations. Documentation, licensing, and downloads available.

Web interface for simplifying the creation of GAMESS UK input files and the processing of the output files.

Molecular Design Software Suite for Irix, Linux, and Windows. Includes features such as structure generation, molecular mechanics, conformational search, molecular dynamics, and similarity analysis. Free for academic users.

The "Massively Parallel Quantum Chemistry Program". Computes properties of atoms and molecules from first principles using the time independent Schrödinger equation. Free, available under the GPL.

Web interface for the quantum chemistry packages MOPAC, Gaussian, and GAMESS. Free version available for download; pro version also available.

Open source quantum chemistry program for atoms and molecules using the quantum Monte Carlo method.