Thanks to dooglus recent convert types (Random, Time Loop and Reciprocal) and the modification he did with the Duplicate layer command now it is possible to create particles simulation in Synfig. To be able to use that convert types and improved features you should use svn r1240 or higher.
All you need is download the following file and use it as the original of you new animation or as an Imported canvas in an existing animation.
If you import the file you would like to change its parameters. To do that, just export the canvas (right click -> Export) and you can access to the ValueBase Nodes at child dialog once you open the exported canvas using the Canvas Dialog. Also you can pick up the particle template layer and place it at your own animation canvas level. It will keep the linked parameters to the imported canvas. It would allow interact with the Z depth of the particles easily.
Structure of the particle template
If you open the particle template file you'll find a inline canvas called "particles". Inside it there are 40 inline canvases called "particle template" and one "Inline Canvas". The last one is only used to hold the background and the green circle.
Each one of those "particle template" Inline canvases hold each particle. Inside of each "particle template" there is a Circle Layer that is the particle itself. The "particle template" only transform its origin properly and the Time Offset of the layer(s) that holds.
You can expand the Origin parameter of the "particle template" Inline canvas and see how complex it is. I'm not going to explain how it is done and hope you don't want me to do it. But if you're so curious you can ask at the Talk area of this page and I'll do all my best.
Same happen with the Time Offset parameter of the "partile template" Inline Canvas.
Parameters of the particle template
The particle itself
In the template, the particle is a circle. You can place there what ever you want. A bunch of layers, an exported canvas or an image sequence. There is only one restriction: They have to be inside one "particle template" Inline Canvas layer.
Number of particles
The number of particles is not a ValueBase Node. In fact the number of particles is the number of times you duplicate one single "particle template" Inline canvas. So you really only need one "particle template" layer to start your own particle set. Notice that the particle-template-v1.0.sifz file have 40 "particle template" layers. All they come from the duplication of a single one. Also each one can be used as a seed for new particles. You can use any of them for your own animation. So, you can pickup one of them and copy to your canvas from the imported particle template file, or use it directly just deleting the other 39 and starting a new particle set.
I strongly recommend that the experiments were done with a small amount of particles (50-100). Later at final render you can duplicate the particles as many times you need and make the render. Command line render is recommended.
NOTE: When a particle template is duplicated the random stuff of the particle is randomized so each particle is always different form its predecessor.
Parameters of animation
Each single particle position follows a parabolic shot trajectory with damping forces. The equations that governs those movements are here. Beyond the parameters that defines the movement equation there are some other that allow control other particular aspects of particles simulation.
lifetime parameter is the amount of time (seconds) that the particle is moved by the parabolic shot. Each particle repeats a loop where it is suffering a translation by the "particle template" inline canvas of a lifetime duration. Each particle has the same cycle length (lifetime) but different frequency, so you see each particle shot a different moments. In other words: lifetime is the amount of time that the particle is flying. This parameter can be changed but cannot be animated. If you animate it you'll find strange behaviours. You can animate but to work properly it should be constant for a period almost the double of its value.