Avogadro

Avogadro is a free and open-source molecular editor and visualization tool designed for students, educators, and advanced researchers in computational chemistry, molecular modeling, bioinformatics, materials science, and chemistry education. It allows users to build, visualize, and analyze molecules, crystals, biomolecules, and crystalline structures in 3D, with support for reading and writing hundreds of molecular file formats including Gaussian, GAMESS, MOPAC, and PDB. The application includes force fields for geometry optimization, multithreaded rendering for efficient performance on large molecular systems, and a plugin architecture that supports both built-in and user-written Python extensions.