Tiled
Tiled supports orthogonal, isometric, and hex maps, infinite canvases, custom properties, templates, and world files, with importers across many engines.
Why use it
It decouples level data from a particular engine and gives 2D projects a versionable, extensible map-production pipeline.
Where it fits
Use art, animation, audio, levels, and narrative to make the game easy to read and its world convincing.
What to check
Runtime import depends on an engine or community plug-in, and custom-property and coordinate conventions should be fixed early.