LayerEdit is the official level editor for Layerformer, an unreleased game where you can swap into the background and vice versa.
Warning
LayerEdit is currently work in progress. You also really don't have any reason to use it if you arent a beta tester.
Can be found here!
LayerEdit is being created with GameMaker (usually whatever the newest release is). You should be able to just download this repo as a zip, unextract it, and open LayerEdit.yyp in GameMaker.