Houdini ShadowCatcher

This is a Shadow Catcher for Houdini, it was created in Houdini 21, but will work in other versions such as 20.5, with earlier versions the Karma/Solaris integration wasn't quite there yet.
This Shadow Catcher works on the Material level, so it interacts with the scene, it is not composited in at render time, you are able to see the Shadow in refraction's and reflection's, it is very fast, taking less than a second to generate on a 24 core 4ghz CPU with the highest quality setting and much faster at lower quality settings.
You have complete control over all the Shadow and Ambient Occlusion attributes, like intensity, fall off, quality, number of light rays and the ability to rotate the environment around your objects.
All you need is a Grid to catch the Shadows, an Environment image (eg. HDRI) to cast the rays and Objects you want to cast Shadows from.