I created a small free snow effect for Gdevelop. It's not perfect as it's based on one huge animated image (you can apply on a separate layer or above other objects with zdepth). It is also in 1280x720. You can adjust to other resolutions by scaling the object in gdevelop.
GDG example file and image resources: https://mega.nz/#!mkx3RCzS!nekXdAnXpY9f ... 21WPVKoe0Q
License: Public domain for all image files you may use, redistribute, do anything (legal) you like with this. Attribution, while appreciated, is not necessary in any form what so ever.
.gdg File may be otherwise protected by editor license, I'm not sure about this.
Snow effect comes in a few forms:
This won't look the same in gdevelop (over your scene instead of just black color), and you will have the ability to configure some things (speed, opacity, even color, etc) yourself to get the desired look.
Below are some expansions to this pack (of course, also free and under the same license)
Accumulating snow effect: