There is only one file type that uses the .MGMF extension:
MindGenius Map File
Mind map file created by versions 2-3 of MindGenius, a conceptual diagramming application; saves a diagram such as a flowchart, brainstorming map, or a strategy plan; used for business documentation and presentation materials.
MGMF files are saved in proprietary binary format. However, MindGenius version 4 uses an open XML format and saves mind maps in .MGMX files. MGMF files can be converted to MGMX files in MindGenius 4.
Updated: October 15, 2011