I recently began working on a volumetric effects shader. It works by integrating over a scalar field (sort of like...rendering a density function), and makes it possible to create many new effects that would otherwise be very difficult or impossible to approximate with particles/billboards.
The pictures posted here only scratch the surface of the kinds of effects that can be created; the main limitations are how creative a scalar field you can come up with, and how computationally expensive it is.
I plan on using the the shader in my current project to replace the some of the more computationally expensive effects, but I am thinking about putting it in the asset store.
Were I to do that, the shader would have to be polished, documented, and I would also have to implement a bunch of common effects. To that end, is this something anyone would like to see in the asset store? And if so, what kinds of 3dscalar fields would you like to see? (For those not familiar with scalar fields, wikipedia does a decent job of describing them: https://en.wikipedia.org/wiki/Scalar_field