ngSkinTools is a skinning plugin for Autodesk Maya, introducing new concepts to character skinning such as layers, any-pose-mirroring, enhanced paint brushes, true smoothing, and more.
A full featured open source plugin, MEL script, and C++ utility library for skinning or smoothing meshes and many conversion and computational geometry functions
mirrors skinCluster, Geometry and more - based on the edge flow of the polygon object. This means, the character could even be in a different pose for the plugin to still work. It also contains commands for easily creating other mirror tools