Maya has it own Ghosting tool, that shows semi-transparent animated objects in the scene which can give an overview of the animated motion you are creating.
Brian Horgan has taken this a step further by creating an onion skin or ghost tool for Maya that will create ghosted outlines of your animation in the Maya viewport – actual 3D outlines of anything that you select. bhGhost is a really clever little tool which will create a composite mesh of your animated character and then uses the standard Maya Toon Lines to create the outlines.
Here’s a video showing the new features I’ve added to my bhGhost tool and showing some typical workflows and uses of it
Brian has put together a little tutorial for his bhGhost tool for Maya showing how to get it going and how to start working with it on animations, and mentions some tips for working with bhGhost, particularly the fact that bhGhost only works on polygons. The bhGhost Tool for Maya is available on Brian’s site here.