What is the addon that when you have the toolgun out it has a grid and you can hold E to snap to a place?

Please answer I am trying to build in single player but if its a ZARP only thing and its custom I understand

What is the addon that when you have the toolgun out it has a grid and you can hold E to snap to a place? Please answer I am trying to build in single player but if its a ZARP only thing and its custom I understand