The HTML5 simulations are the best place to start - they should work on all modern browsers and mobile devices. This collection (mainly aimed at introductory physics) currently has over 200 simulations, with more in the pipeline.
The remaining collections are mostly Java simulations - those are getting very difficult to run these days, but I'm leaving the collections accessible because some people can still run them, and there are quite a few simulations there. The goal is to eventually reproduce most of those in HTML5 - that has been done for many of them already.
There are three main collections of Physlets. Each collection can be viewed via the menu at left. The collections cover Physlets used in a typical first-semester introductory physics class, Physlets used in a typical second-semester introductory physics class, as well as our collection of prelab assignments that use Physlets.
There are also some good simulations in the collection based on the Ejs (Easy Java Simulations) package from Francisco Esquembre.
The simulations and animations were scripted by Andrew Duffy at Boston University. Please direct any questions or comments to firstname.lastname@example.org
The Physlet simulations and animations found here are based on Physlets from Davidson College. Have a look at the Davidson College Physlet Archive to see all the wonderful things you can do with Physlets.
The Ejs (Easy Java simulations) are based on the Easy Java Simulations package created by Francisco Esquembre.