To clarify a few things, the point to Spriter is its specifically for making animations for games. This will overlap into game related data such as triggering variable changes, sound effects, placing collision rectangles,image points etc.. all at any key frame(s) in a very natural and visual manner. (once these features are implimented). The other hugely important point to Spriter is it can save out actual animation data, which can then be used in a game engine to recreate the tweened animations using just a tiny bit of data and the original "body part" images. This can save insane amounts of file space and ram, allowing you to fit drastically more animations (and all perfectly smooth and tweened) as compared to using full frame sprite sheets etc.
There will also be a super easy "character map" system, which will allow you to swap out images with other images on the fly, to super easily and efficiently create character variations (like changes in weapons and armor etc.) at runtime in your game.
Of course, to do this, you need a plug-in for your game authoring system of choice (mine being Construct 2!) to allow for the actual replay of Spriter animation files.
One such plug-in is being worked on For C2! Edgar will post about that shortly!
One last note. Spriter is still very early in its development so its useability will be getting drastically improved over the next several weeks. If theres a feature you really want to see implimented or changed, please let us know in our forums at http://www.brashmonkey.com/forum
Mike at BrashMonkey