[ry454]

In fact, it's a really simple app: a height map on a sphere approximated with triangles. With a bit more extra complexity, the app could do raymarching on a interpolated height map: this would remove triangle artifacts around "cliffs" on the height map. It would still be real time 60 fps even on smartphones.

To do something like this, you need to know a bit of WebGL and a bit of JS. No frameworks really needed at this level. The best guide to WebGL I know of is this:

https://webgl2fundamentals.org/

Complexity starts when the height map isn't enough and you want to make arcs or otherwise arbitrarily shaped structures. This is where you'd need a framework, unless you want to implement all the math and glsl yourself.

And as always, the idea is really the 1% of the work. Anyone can say "it's just a height map on a sphere". 99% of the work is materialising the idea, debugging glsl, fixing ugly bugs on smartphones and esotheric browsers, dealing with partial WebGL API and so on.