Lately I came across this already Kickstarter-funded project, called “Spriter”. It is an “easy to use animation tool”, especially suited for game-designers. The tools uses a modular method of animation – instead of each frame being a single complete image, the frame is constructed from many small, re-useable images (for example body parts). Each of these images that are used to construct the full frame can be scaled and rotated to further increase reuse of content.
The developers at Brash Monkey promise, that with Spriter you can create robustly animated game characters and effects with a workflow that’s “highly intuitive, visual, and efficient for not only time, but also for the final game’s file and memory usage”.
Let’s wait and see, if there will be also a version available for OSX at any later time.