If you mean separate windows like... almost nothing uses separate windows nowadays...
Like Gimp default layout?
No, currently does not support that, there is a request for the editor to be able to have separate windows, a feature like that could be useful for non-game projects.
I think most game engines do not support that because main gaming platforms are for a single screen/window.
Try with SFML or SDL, not sure about Lime/OpenFL and game engines that work over them.
Of course, you can dig into Godot source and try to make something, the same for Unreal.