Everyone who uses Unity knows about the editor. It's the core place where you will spend a great deal of time putting your game together. You will spend the rest of your time in the choice of your code editor, patching things together, adding values, and working around with what most see as limitations of the editor itself. This, however, is not the case.

The people at Unity realized early that they couldn't do everything, since everyone wanted something different or little tweaks here and there; if they had tried to do everything, nothing would have ever left their doors.

So, from the ground up, Unity was designed to be extensible, and they exposed much of what is needed to build your own editor in effect within Unity itself.

If you browse the asset store (https://www.assetstore.unity3d.com/en), you will see a lot of assets that take advantage of this, and they have produced some really snazzy bolt-ons for the editor. These can reduce the need to code and just build things...