gimp-spine exports GIMP layers to PNG images and outputs a Spine JSON file for easy importing. Spine is a 2D animation program that lets you rig images to bones like you would in 3D animation. This GIMP plugin is useful when starting a new Spine project because Spine can start a whole new skeleton with the images in the right positions and all you need to do is add the bones. To see how the import workflow would work, check out Spine's run animation tutorial video.
To install, put gimp_spine.py in your plugins directory.
To use, open up GIMP and select File -> Export to Spine from the menu.