This is an Image Effect used to create Crepuscular Rays.
This goes a little further than the intrinsic Unity3D version, you are able to use your own texture for the light source, you can place it anywhere in a 2D or 3D scene using the intrinsic Lights that come with Unity3D, the effect will use the light's colour, intensity and scale to render the light source and then from its position render the light rays. You are also able to rotate the source texture.
The Asset comes with both a 3D and a 2D sample showing how it can be used.
This effect can be applied with both the Forward and Deferred render pipeline and can be used in both 2D and 3D (orthographic and perspective) views.
This can be used as mentioned above, to cast sun shafts into a scene, or, you may for example, have a magic item you would like to have radiate light shafts, this effect will manage that too.
Note: The GPU it's ran on MUST support Depth Textures. It has only been tested on PC under Windows 10