This is my first post on these forums, I signed up just to comment on your post.
I've downloaded & watched your videos & based on what I saw this is an excellent tool. Per frame animation is preferred over something tween based, I've been looking (and have found) tools like this one in many places across the internet, all of differing features. I have a few suggestions for your tool.
By the way, my interest in this tool would be strictly for animation purposes, apart from needing to integrate it into an engine or game.
I'm not clear on if this already exists or not, but replacing images within an animation, like adding or subtracting parts (like say a head at differing angles). If it doesn't already exist, it's a must.
For the Part Info: dialogue (when importing lone images), one feature you could add (& it isn't necessary but it would be incredibly useful) is Mesh Deformation.
Onion Skinning would be a preferable feature (choose number of frames shown & which frames, like forward and/or back).
Not sure this exists either- Export frames or save as animation images, for example a series of GIF's or PNG's sans the data hierarchy: not the pieces, but the whole character frame images (with background transparency, possibly resolution options).
All that said, your application would be very useful to allot of people, please let us know of your progress.