With Snowify you can easily turn your game into a winter wonderland.
This easy-to-use tool generates snow-meshes for your assets, automatically unwrapped and textured.
You have complete control over the snow's thickness, angle, and various other settings.
Works with Unity and Unity Pro.
note:
-The jeep, f16 and house in the screenshots are not included in this package, but are available for free on the unity asset store: jeep, f16, house
-It can be set up to not create snow in covered areas, however, this is an approximation, and the result will depend on the topology and detail of the source mesh.
-Does not work well with transparent objects, because the snow is generated based on the source object's mesh.