Avogadro

Avogadro is an advanced open-source molecular editor and visualiser tailored to the needs of computational chemistry, bioinformatics, molecular modelling and materials science. It runs on Windows, Linux and macOS, supports multi-threaded rendering, and features a plugin architecture that enables developers to extend its capabilities (for example via Python scripts or C++ plugins). Avogadro serves a wide audience—from students who need to build and visualise molecules easily, to advanced researchers assembling input files for quantum chemistry packages or analysing molecular output. The project is supported by the community under an open-source licence (the current codebase uses the 3-clause BSD licence) and is actively developed within the Open Chemistry framework. GitHub+1 It is also listed as a supported application by the SBGrid Consortium for structural, chemical and materials science research. sbgrid.org As for pricing: Avogadro published under MIT license, is free of charge, there is no paid licence or subscription model—users can download and use it without cost.