Shugan

Shape Keys ++ is a Blender add-on from Shugan for managing shape keys, covering duplicate, mirror, invert, blend with vertex groups, global sliders, and applying shapes to basis, all without switching modes.

Weight Paint ++ is a Blender add-on for managing vertex group weights. It detects asymmetric vertex groups and weight islands with a single click, then provides panels to repair symmetry, clean up groups and transfer weights.