There is only one file type that uses the .NM3 extension:
Navitel 5 Map File
Map file used by Navitel navigation software 5.0 or later; replaces the .NM2 file used by previous versions of Navitel Navigator; contains map data such as roads, landmarks, GPS coordinates, natural geography, and other map features.
Navitel is primarily used in Eastern Europe and Russia. Some features include 3D graphics and real-time traffic updates.
Updated: May 1, 2013