PhET Interactive Simulations - https://phet.colorado.edu/
(PhET Interactive Simulations) is a project of the University of Colorado at Boulder, which is an open educational resource with detailed explanations. Founded in 2002 by Nobel Prize winner Carl Wiman. Phet's main goal is to improve the learning and teaching of science. Their mission is to "advance science, math literacy and education through free interactive simulations around the world."
"PhET" in translation from English means "Technology of physical education". The project is currently developing, improving and making available to the public more than 125 interactive simulations for educational purposes in physics, chemistry, biology, earth sciences and mathematics. The simulations (experiments) have been translated into 65 different languages and in 2011 alone the website was visited by over 25 million people.
PhET's interactive experience design team is based at the University of Colorado Boulder and is made up of a 16-member team consisting of professors, doctoral students, academics, educators, programmers, and administrative assistants.
PhET interactive simulations use science-based experiments to help you learn the science and mathematics. Simulations (interactive experiments) can be used in lectures, experiments or as homework assignments. Its advantage is that simulations can be easily downloaded to a computer and used even when there is no Internet connection.