I apologize for being a bit late, but I thought I'd mention there's work in Blender to make a sprite animator, which is notable because it's free and open-source.
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While this system wouldn't directly interface with AGS (which was the original dream), Blender could obviously export to PNG or something. The project isn't currently done yet (February of 2016) but I thought I'd mention it as a potential free alternative.
The game engine, Godot (which is also free and open-source), also has an exceptional sprite animator, but there is currently no way (that I know of) to export the animations out of the engine (like in PNG format). The same video creator,
Andreas Esau, has a great Godot video tutorial series, which is how I learned about the Godot engine and sprite animator.
visionmind