Spine Runtimes are software development kits (SDKs) that enable game engines to load and play Spine animations. Each major game engine (Unity, Unreal Engine, Godot, JavaScript/Pixi.js) has an official Spine Runtime that handles parsing Spine files, skeletal deformation, animation playback, and events. Using a Spine Runtime, you can load a .atlas and .skeleton file, create skeletal mesh components, play animations, and control them from code.