It's using Three.js[^1] with Photons[^2], and a number of other interesting libraries for calculation like satellite-js[^3].

[1]: https://github.com/mrdoob/three.js/

[2]: https://github.com/mkkellogg/Photons

[3]: https://github.com/shashwatak/satellite-js

I don't know which framework they're using, if any, but this is WebGL2. You can write fairly modern OpenGL code and run it in the browser. :)