Spine - Spine is 2D animation software designed specifically for software and game development.
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!
Live2D Cubism - Live2D is the world's first drawing technology to enable 3D rendering of 2D images.
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Synfig Studio - Just another WordPress site
LibreSprite - Free and open source program to create animated sprites.