This is a demo of the Unity Particle Pack available in the Unity Asset Store. Below is the description:

A set of sample particle assets to use in your games, and to help you understand how to achieve certain effects using the Unity Particle System component and modules. You'll find Fire, Explosions, Rain and other cool effects here all for free! Note: this pack is new for Unity 5.5 and as such is only for use in version 5.5 and above.