Algodoo

its pretty good, im not a big fan of spring engines my self, but this is good

id make spawn engines, but i SUCK AT SCRIPTING lol

its easy to make a spwan engine, just copy and paste in a code for spawning circles.
I don't konw if I've released any of mine, but here is a script to get started.

(e)=>{
scene.my.addcircle({
pos := e.pos;
radius := 1;
killer = false;
mass = 2;
collideset := 1;
color := [1.0, 0.0, 0.0, 0.3];
drawborder := false;
drawcake := false;
restitution = .5;
friction = .5
})
}



Simply change the different variables to make it yours.
To change the collision set, make a new object, set it to the desired "ABCDEFG" layers and check the scripted collideset. For instance, A & B is combo #3
collideset := 1; <------------



Hope this helped! Good luck!