Avogadro is a molecule editor and visualizer designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It is extensible via a plugin architecture. Molecule builder-editor for Windows, Linux, Unix, and macOS. All source code is licensed under the GNU General Public License (GPL) version 2. Supported languages include: Chinese, English, French, German, Italian, Russian, Spanish, and Polish. Supports multi-threaded rendering and computation. Plugin architecture for developers, including rendering, interactive tools, commands, and Python scripts. OpenBabel import of files, input generation for multiple computational chemistry packages, X-ray crystallography, and biomolecules.