This is a list of places on the vast internet where you can learn about science and/or math. Be sure to try removing parts of the url (ex. site.com/a/b -> site.com), checking github repositiories, and clicking links to see more stuff. Many sites here are pretty interactive and a fair amount are sandboxy. all of these are free. Also, if a site has a * on it, that means it's probably dead (not updated).
general stuff
literally this site explorable explanations* falstad's site testtubegames phet, but it's the dev directory concord consortium Physics Educational Software for Your Browser (yes that's the official title)* Dissemination of IT for the Promotion of Materials Science Teaching & Learning Packages (I finally kinda understand what this einstien summation thingy is yay)* more explorable explanationsquantum physics
a dirac equation simulator quantum circuit simulator quantum flytrapchemistry
chemagic moleculesbiology
well, there's basically no biology simulator out there, so just have chemagicoptics
ray optics simulatorfluids
2d water (and air)