3DM

OpenNURBS is the file format used by Rhinoceros 3D to store 3D models. It is developed by Robert McNeel & Associates, and specifications and libraries are released for free usage by the company.

OpenNURBS is an open source toolkit for reading and writing 3DM files. The OpenNURBS Toolkit provides CAD, CAM, CAE, and computer graphics software developers the tools to accurately transfer 3-D geometry between applications.

Unlike other open development initiatives, alliances, or consortia:


 * Commercial use is encouraged.
 * The tools, support, and membership are free.
 * There are no restrictions. Neither copyright nor copyleft restrictions apply.
 * No contribution of effort or technology is required from the members, although it is encouraged.

Libraries

 * C++: OpenNURBS SDK
 * C#: OpenNURBS SDK

Sample files

 * https://telparia.com/fileFormatSamples/poly/openNURBS/