I am going to port an old unity game I started on to Defold. Unity allowed me to extend the editor to kinda streamline certain aspects of levels in my game. For example I made an easy way to make waypoints an NPC would follow by just clicking a button which would create the waypoint parent object and add waypoints under it that I could drag around and order, I would click an add waypoint button and drag it to where the next point should be. Another example is pairing two objects, one is a trigger and another is triggerable, when you would click on the trigger in the hierarchy it would paint a debug line to the triggerable object it is paired with so you could easily see what that trigger does.
I’m sure someone could think of some other examples but is there some example of extending the editor?