Molecular Workbench is “a free, open-source tool that delivers visual, interactive simulations for teaching and learning science and engineering.”
I found that it only took a few seconds to install the program and I was up and running with several quality simulations at my fingertips. (You can also download a fully offline version also.)
There are demo simulations organized by categories such as- Fluid Mechanics & Heat Transfer, Molecular Dynamics, and Quantum Mechanics. There is a Library of Models that can be used to author your own simulations as well as an Activity Center with several shared activities for learners of biology, chemistry, and physics concepts. I will admit that I have only an emerging understanding of this resource but there is a lot of potential here. I would love to get some comments from teachers who have used Molecular Workbench extensively with students.