Tiled Map Editor
Tiled is a free software level editor. It supports editing tile maps in various projections (orthogonal, isometric, hexagonal) and also supports building levels with freely positioned, rotated or scaled images or annotating them with objects of various shapes.
Even though Tiled is available for free, I accept voluntary payments in order to be able to spend more time on it. I'm currently spending two full days/week on Tiled, which is possible thanks to people choosing to pay for Tiled here as well as those supporting me on a recurring basis through Patreon.
I did not quite reach my funding goal yet, so if you enjoy using Tiled and are able to chip in, please set up a small monthly donation through Patreon. Thanks!