Skysim is a sky and volumetric atmosphere addon for Blender.
what you'll get :
-Pure rayleigh sky shader that run on GPU
-2D and 3D Volumetric clouds layers
-Infinite ground layer
-Ground fog for atmospheric scattering
-Everything controlled in a single panel
It let you produce stunning atmospheres from sunrise to sunset without having to tweaks tons of settings.
It is based on the nishita osl sky shader and inspired by this article.
The sun disc rendering is based on the frostbite engine technique.
Just rotate the sun and the addon will make the perfect sky according to the sun position.
You can produce godrays in seconds and enhance your scenes with a real feeling with the volumetric fog.
you can add 2D and/or 3D clouds and animate the position of the sun, the clouds, almost everything.
It can be use to render outdoor ans indoor scenes, it's a full replacement for HDRI files, but it use only 1% of the memory of HDRI ! (never goes over 50 Megas when HDRI's use Gigas !!) and is faster to render.
Limitations : It is for Cycles ONLY !! the sky shader is too complicated for Eevee. Eevee can still be used to tweak the volumetrics but the background will not render (same as the texture sky node).
The goal is to achieve atmosphere photorealism.