The PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education research and engage students through an intuitive, game-like environment where students learn through exploration and discovery.
Copy & paste the above command to any Unix-based system to begin download. Rsync can pick up where it left off and only downloads changes.
It's the most efficient way to stay up-to-date with RACHEL modules.