extractDeltas is a plug-in for Maya which helps with the creation of corrective blend shapes to improve the overall deformation in conjunction with regular skinning.
It allows to model the corrective shape based on the deformed pose of a character and then generates a mesh which can be used as a blend shape target before the skin cluster calculation is performed.
extractDeltas is an important tool for creating corrective blend shapes but also requires some manual work.
If you are looking for a way to streamline your blend shape and corrective shape workflow check out SHAPES, a blend shape editor for Maya which combines a variety of tools for your everyday work.
SHAPES is free for private and evaluation purposes. Visit the SHAPES page.