An interesting effect could be this animation where the particle flips horizontally on itself

Mouse could become a light source to have particles with a shadow based on mouse hover or click (for a static light source) like in this sample

Particles could explode on click or when collisions are set on destroy like in this sample

Actually trail is made by covering the canvas by a semi-transparent rectangle, its transparency is something like 100/value but the result can be a dotted trail instead of a continuous line.

A drawn trail could give a better result, but we should consider performance too. The length is how many position should be kept to draw a multi-point line (or multiple lines).

Cover color will become obsolete if this way is taken