I turned the drawing tool for my new app into an animation tool.  It's a bit idiosyncratic, and geared towards the type of animation I want to use in the app, but it's online and could be used with some guidance.

Right now you can basically draw, add frames, copy and paste.  When you click to go to next frame or last frame it automatically save drawing on current frame.  All of the buttons have key commands so I can draw with right hand and operate the program with my left.  Maybe will make tooltips at some point, though I doubt anyone else will really use it.  Eventually want to add layers, frame timeline and erase functions, but that sounds hard....

http://owenroberts.github.io/lines/animate.html