The average new user joining the Assetto Corsa community has a rough time understanding the different mods and apps available.Are we sure this functionality is in the payed CM, I always thought it was only in the Patreon version.
CM - Content Manager: New UI / Launcher replacement that is the best thing since sliced bread. A must have because its that good. Has a "lite / free" and "premium/donateware" version. No it does not bring rain, neither lite or premium.
CSP - Custom Shaders Patch: A mod/patch that adds more to the game, such as 24h lighting cycle, new features, etc. The public versions of CSP do not bring rain. There's a Patreon set up by X4Fab that will give its supporters *preview* versions of CSP that will bring the rain module - notice I said module.
SOL - Public mod of a new weather system that utilizes CSP 24H lighting cycle - creating different types of weather, etc. If using CSP Preview versions, it will provide wet weather conditions (rain)
Pure - By the creator of the SOL mod, behind a Patreon paywall, this weather system is similar to SOL but more lightweight, better built from the ground up, and includes incredible high resolution and photorealistic skyboxes (SOL only provides 3D clouds), it will also provide wet weather / rain conditions when using CSP Preview versions.