Tile Studio - Complete development utility for graphics of tile based games.
Sprite Fusion - Design your game with Sprite Fusion, the ultimate free online tilemap editor. Design 2D games with ease, direclty export to Unity Tilemap and Godot Scenes. Ideal for retro games!
LibreSprite - Free and open source program to create animated sprites.
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Piskel - Piskel is a website where designers online create sprites or pixel art.
Tiled Map Editor - Tiled is a general purpose tile map editor.