There is apparently a 3-D modeling format called Mesh that is connected with New York University (NYU) and uses a .m extension; this is one of the formats that shows up in lists of file formats but is difficult to find any details about. A forum discussion answering a question about how to save files in that format says "You need to get the .M specification from the university and convert the data you loaded into OpenGL into that format." So easy peasy; just get the spec from the university. It doesn't specify just who at the university might have this spec, and nothing seems to be turning up in NYU websites. NYU Data Services helpfully gives a guide to file format selection for academic projects that fails to make any mention of the format. The NYU Geometric Computing Lab does various projects involving 3-D meshing, and has some downloads of mesh files, but they don't seem to be in this format. Further research is needed.