To help more on Scirra, I want learn from the 0 and build up a tool where you'll can manipulate various images, selecting them all from your Explorer, and them, export it in a sprite strip, ready to be added on the animation menu.
How it work:
In any browser, you'll have the opportunity of import with a multi-selecting upload button your sprites to the tool.
One time uploaded the content, you'll be ready to manipulate the mosaic of sprites, crop, re-size, align, zoom, move, mirror, add effects, ghosts, change his colors, opacity, and (if I learn it at this stage) swap specific colors, then, export it in a strip of sprites.
A time ago, I saw somewhere a tool where you can read gif files and convert them to a mosaic (Game maker?), it's possible, and I'll learn how.
So, I hope you liked almost one of my tools and I wish you to desire the best for this tool, because it'll be freeware and opensource, made just for help you.
Old Sprite Organizer:
Zip your sprites splinting each frame in one new file, organize they by name or select them in order, upload and they'll be organized aligned by the middle bottom. I tried to learn AS3 to improve my tool, but C2 come out and I released it as it is now.