Links to other collections of science interactives. Get ready to get lost in more lists.
If any links are broken, let me know. 
PhET
The definitive collection of free online resources for physics classes. Run by University of Colorado Boulder.
Astro Apps
Collection of interesting astronomical and cosmological simulations, created by Haus der Astronomie.
Index of Simulations
A spreadsheet pulled together for teachers of a categorized list of hundreds (wait, thousands!) of simulations you can find online, sorted by topic. An incredible resource organized by Helen Reynolds.
PBS Learning Media
Collection of various science learning resources hosted by PBS LearningMedia. Covers topics such as physics, biology, and geology.
A Free Particle Interactives
A set of Desmos simulations covering a wide range of physics including many about mechanics – an excellent resource for teachers and students. Created by Michael Freeman.
Tesseralis
Set of simulations and explorables about math, created by Nat Alison.
Universe & More
A collection of interactive physics resources that are fun and easy to use. By Matthew Blackman.
The Physics Classroom
Sets of pages with lessons and interactives about a variety of physics topics.
myPhysicsLab
Lots of small simulations of things like pendulums and springs, where you can easily change the values, too. By Erik Neumann.
The Falstad Collection
Collection of small simulations created by Falstad.
ScienceGameCenter
THE definitive list of science games – both digital and physical. Curated by Dr. Melanie Stegman.
Ricky Reusser Collection
A lot of cool interactive math-y explorables to check out. Created by Ricky Reusser.
Dan Schroeder Physics Educational Software
Physics education software created mostly by Dan Schroeder, some excellent simulations in here.
Fowler’s Physics Applets
Collection of small physics simulations, many including nice explanations. Built by Michael Fowler.
oPhysics
A large set of interactive physics simulations built by Tom Walsh. Covers a wide range of physics, including forces, waves, and light.
Concord Consortium List
A collection of science interactives by Concord Consortium.
Red Blob Games
A variety of interesting lessons, simulations, and explorables about topics in math, physics, and programming. Created by Amit Patel.
Explorable Explanations
A collection of Explorable Explanations curated by Nicky Case.
Academo Collection
A collection of small open source physics simulations, created by Academo.