I came across a software called Sound Particles on a sound design forum. It's a cool 3D sound design tool that uses particle systems to generate sound atmospheres.
What it means is that you can import several sound files from your sound library, then tell the software how they will appear in a virtual 3D environment around your virtual microphone(s), add some random qualities and after rendering you get a rich soundfield.
There have been other software using the same idea of particle systems, but Sound Particles seems very sleek and easy to use. I would imagine that it would be excellent for quickly creating big nature sounds such as storm approaching or birds flocking, but also unnatural experiences.
I've now been testing Sound Particles for a couple of times and there are a few attributes I don't know how to set or if they even can be adjusted. For example even if I import 50 different sound files I get the same handful sounds repeated too often, which degrades the illusion of a huge mass of individual sounds. Well, there must be an adjustment for that, but so far I haven't found it. And there's no manual, only video tutorials! So, so far my results haven't been very impressive, but this is something weird I managed to get out of the programme after a few attempts: