Various emitters
Emitters are a collection of moving particles that can be spawned from a brick, to create many interesting effects like fire, water, smoke, bubbles, and even grass.
Usage
Emitters are very easy to use, just use your wrench tool on any type of brick (excluding special types like a music or vehicle brick ) and choose an emitter from the middle tab in the wrench section. You can change the direction that the particles will go by selecting either Up, Down, North, East, South and West.
The brick properties window where you can, amongst other settings, choose an emitter, and change the direction.