It has already been posted by jeffschofield, but the original is here[1], along with a brief article breaking down the effect[2].

The one you posted is in many ways nicer though due to it all being a single shader, however it has the downside of the drops not interacting with each other.

[1] https://tympanus.net/Development/RainEffect/

[2] https://tympanus.net/codrops/2015/11/04/rain-water-effect-ex...