Avogadro - Education/Science App

http://avogadro.openmolecules.net/

Avogadro is an advanced molecular editor designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It offers flexible rendering and a powerful plugin architecture.

Cross-Platform: Molecular builder/editor for Windows, Linux, and Mac OS X.
Free, Open Source: Easy to install and all source code is available under the GNU GPL.
International: Translations into Chinese, French, German, Italian, Russian, and Spanish, with more languages to come.
Intuitive: Built to work easily for students and advanced researchers both.
Fast: Supports multi-threaded rendering and computation.
Extensible: Plugin architecture for developers, including rendering, interactive tools, commands, and Python scripts.
Flexible: Features include Open Babel import of chemical files, input generation for multiple computational chemistry packages, crystallography, and biomolecules.