Free Texture Packer - Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites.
Spine - Spine is 2D animation software designed specifically for software and game development.
Sprite Monkey - Small and fast but still full-featured sprite sheet editor.
Synfig Studio - Just another WordPress site
ShoeBox - Free unlimited photo storage, so you can rediscover your photos anywhere. Available for iPhone, iPad, Android, Mac and PC.
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.