This is Minecart Physics.

A map with Minecarts. (Like you never guessed that)
They pour in.
They create a flow, like water... But more versatile.
Its versatility is superior.
It can cover any terrain.
Even oceans... If you give it time.
You can play with the flow with such:
Cows
Explosions
Ruin The Flow
It is a sandbox for Minecarts out there. At least for now.
Now download this map and see what they form!

Note: 
Clouds Off
Render Distance 8+
Low End Computers, Proceed With Warning*
*Mass Frame Drop