your question makes sense. as you can see - Juggler is in animation/ package in source tree. but i see that classes are not put into some packages in PIXI, like PIXI.animation.Juggler . i cannot name it TweenManager, because Tween is actually only one of it's clients. in API you can see there are also calls for delayed and repeated calls. in general - it's IAnimatableManager (i wonder where can i describe this one, maybe some empty file...).
another side of the question - if this code can be placed in PIXI ? Starling has it. jQuery has some animation API.