Animatic for iPhone
There are already plenty of cool iPhone and iPad apps that let you bring your artistic ideas, drawings, and animations to life. Animatic for iPhone is designed to make creating hand-drawn animations even easier. It has a user-friendly frame editor and onion skinning. The pro version lets you repeat frames.
Animatic has a simple user interface and lets you export animations to animated GIFs and video. You can try the app for free.