Dont often Scoop Subject specific features but these are utterly astonishing. High quality simulations for Physics, Chemistry, Biology, Geology and Maths.
Amazing variety and variation within simulations. Models are chosen well eg Conservation of Energy from KE to PE is based on a skateboarder on a ramp. Options for this include energy transfer to Heat via friction.
The electrical circuits model also allows you to explore pupil misconceptions with ideas such as pd and current
Many simulations also include graphical analysis and you can choose a range of ways to present the information
See on phet.colorado.edu