Most of the 3D and compositing packages offer some sort of a particle systems toolset. They usually come with a nice set of examples and demos showing all the stunning things you can do within the product. However, the way to really judge its capabilities is often not by the things the software can do, but rather by the things it can not. And since the practice shows it might be not so easy to think of all the things one might be missing in a real production at a time, I have put together this checklist.
Flexible enough software allows for quite complex effects
like this spiral galaxy, created with particles alone.