There is a stat in the base game that allows you to set the jump height multiplier: jumpHeightMul 

You cannot use this multiplier, however, to make jump height lower than 1, because the game bottoms the jump height at a minimum of 1. 

This mod makes it so a lower than 1 jumpHeightMul will apply correctly. The mod itself doesn't do anything on its own, but having it will remove the limiter. It is meant to be used by developers.

For example, I am going to use it to make a mod that makes armor reduce jump height