PolySmoother is a professional tool to efficiently work with Smoothing Groups.
PolyUnwrapper is a complete set of professional tools designed for the texture artists, especially for the architectural and game industries.
Advanced UV Normalizer is a tool for normalizing the Texel Density across different objects.
XFormer is a tool that will allow you recover the transformation of an object.
QuadSphere is an Object Plugin that creates spheres made of quads, which are useful for low polygon modeling and mesh subdivision.