This is an After Effects script meant to implement a function similar to Justin Barrett's TweenMachine Maya script.
Creating breakdowns in character animation is one of the most critical steps in making good animation great. With this tool, you simply select the two keys you want to breakdown, place the time indicator (playhead) at the location you want the breakdown to be created, and choose a proportion between the first key and second keys. Click Tween! and your breakdown is created.