Animation Desk allows you to create animations, drawing cartoons or just some light sketching when you're on the go. Available on OSX, iOS, Android, WP and Windows.
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Pro Photoshop compatible
Supports PSD file import/export, can export your draft to Photoshop easily for further works.
Pro Free to use
Some features may require purchases but the app free as is, and works fine.
Pro Quick sketch
Great for light sketches, and some drafting for your animation.
Pro Works on different platforms
It supports almost every major platforms, so working on iOS and Android devices is not a problem.
Con iOS free cloud version has no sound options
Con Android version is not as extensive as the iOS version
Some of the options that are present in the iOS version of Animation Desk Cloud aren't integrated in the Android application. For example, features such frame labeling and the eyedropper tool aren't available.