This is inspiring, a client side tool like this to compose press-kits would be nice for media O.o
Incredible, I literally started making a client-side gif animator like this on Wednesday. I'm kinda glad I didn't try to finish the whole thing yet, as this is very well done. I didn't know about that cool GifEncoder.
Tech: HTML5 drag n drop, FileReader, a[download], GIF encoding on the client, BlobBuilder, postMessage, <input type=range> (with Firefox polyfill), appcache, transforms, etc. Oh! and the aforementioned * { box-sizing : border-box; }