Sprite Editor

Piskel

http://www.piskelapp.com/

Aseprite

http://www.aseprite.org/


Simple Sprite Editor

http://sourceforge.net/projects/simplespriteedi/


Explogen

http://gmc.yoyogames.com/?showtopic=211466


Explosion Texture Generator

http://www.saschawillems.de/?page_id=253


TexturePacker

https://www.codeandweb.com/texturepacker

http://haxecoder.com/post.php?id=32


Pyxel Edit

http://pyxeledit.com/