Links to other collections of science interactives. Get ready to get lost in more lists.
If any links are broken, let me know. 
Tesseralis
Ricky Reusser Collection
A lot of cool interactive math-y explorables to check out. Created by Ricky Reusser.
Fowler’s Physics Applets
Collection of small physics simulations, many including nice explanations. Built by Michael Fowler.
Astro Apps
Collection of interesting astronomical and cosmological simulations, created by Haus der Astronomie.
oPhysics
A large set of interactive physics simulations built by Tom Walsh. Covers a wide range of physics, including forces, waves, and light.
Red Blob Games
A variety of interesting lessons, simulations, and explorables about topics in math, physics, and programming. Created by Amit Patel.
PhET
The definitive collection of free online resources for physics classes. Run by University of Colorado Boulder.
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.
Academo Collection
A collection of small open source physics simulations, created by Academo.
Dan Schroeder Physics Educational Software
Physics education software created mostly by Dan Schroeder, some excellent simulations in here.
The Physics Classroom
Sets of pages with lessons and interactives about a variety of physics topics.
Concord Consortium List
A collection of science interactives by Concord Consortium.
Explorable Explanations
A collection of Explorable Explanations curated by Nicky Case.
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.
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.
Universe & More
A collection of interactive physics resources that are fun and easy to use. By Matthew Blackman.