This is an add-on created mostly by me, for my own usage. It offers some handy tools for cleaning up and managing messy armatures imported in .fbx or .dae format.
Tools include easily pruning out non-deforming bones, removing vertex groups with no effect from meshes, identifying small tangles of hand and face bones and moving them to separate layers, sorting bones out onto different layers by names, identifying symmetrical pairs of bones by size and location and matching their names so Blender recognizes them as symmetrical, and more.
Works on an armature you have active in object mode. I've been mostly using game models imported as .fbx, but as near as I can tell, .dae and the rest work fine. Also, make sure all the bones you care about affecting are in the first armature layer.