FileInfo.com - The File Extensions Resource

.3D File Extension

File Type	Stereo CAD-3D Image File
File Format	File
Common?	No
File Description	Three-dimensional image format used by Atari Stereo CAD-3D for storing 3D objects; uses Motorola Fast Floating Point library (LIBF) for storing vertex coordinates.
Program(s) that open 3d files	Windows: quick3D Viewer; quick3D Geometry; quick3D Professional

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/3d