What does it do?
It demonstrates how one can create a game with gravity-ish components.
For doing so, it created a lot of rocks that move downards.
What are important aspects of the code?
These things are key in this demo:
ControlSystem, to move the user around, to avoid the rocks;
RockSpawnSystem, to keep spawning the rocks;
FallingSystem, to make the rocks fall;
DeathSystem, to make sure you'd want to avoid the rocks.
There is no documentation for this package.