The springs are not damped yet, but for the main example, drag is enabled[1]. This continuously slows down the particles.
Drag is computed[2] for all the particles using something similar to the Drag equation[3].
Also, like electricslpnsld said, having a small enough time step helps.
[1] https://github.com/loicbourgois/gravitle/blob/master/fronten...
[2] https://github.com/loicbourgois/gravitle/blob/master/src/par...