PhET is a service that provides free interactive math and science simulations covering topics in physics, chemistry, biology, earth science, and mathematics. It has been popular with science and math teachers for many years. Recently, I learned that PhET has been developing some simulations that offer online accessibility features including alternative inputs for navigation and interactive descriptions.
There are only nineteen accessibility enabled PhET simulations available at the moment and they are all still prototypes. You can try them here.