BodyPaint 3D
From Just Solve the File Format Problem
BodyPaint 3D is an image and texture editor designed for use by 3D artists. Its native B3D format is apparently actually a 2D image format, but the images are intended to be imported into 3D modeling software for use on objects therein (where they are transformed to appear as if they are actually on a 3D object seen with proper perspective and angle).
This file format is unrelated to the Blitz3D Model format or BVE object formats, which also use a .b3d extension.