CGMatter
This addon is bundled with Genie (get it heavily discounted)!
Free Lite version comes with only collider collection, density, and radius controls! Doesn't includes splash controls, direction, and cutoff!
Rain Simulator
Rain simulator is a light-weight setup for photorealistic rain. A fully procedural drag n' drop solution!
(blue/green for visual clarity in gif)
Simulate 100,000's (or millions) of particles in seconds! Solver has been optimized for scene performance and accurate collisions.
(blue/green for visual clarity in gif)
(blue/green for visual clarity in gif)
Control both the rain itself and collision splashes!
Documentation
Colliders (collection) - collection of objects for rain to collide with.
Z Cutoff (float) - z value under which rain will be automatically deleted.
Density (float) - rain particles spawned per area.
Size (float) - radius of rain particles.
Direction (vector) - direction of rain velocity.
Speed (float) - scales the direction vector.
Randomize (float) - add randomization to the direction.
Droplets (integer) - Number of particles generated on splash.
Lifespan (integer) - Average frame lifespan of splash particles.
Speed (float) - Emission speed of splash particles.
Installation
Install like any other addon. Drag the zip right into Blender and hit confirm. The rain simulator will show up in Shift + A > Mesh > Rain