NIF

NIF is the 3D model format used in the NetImmerse/Gamebryo Game Engine, used in such games as Fallout, Fallout 3, and Skyrim. There are some tools available to deal with it. Files start with ASCII 'Gamebryo File Format'. It seems these files are compressed.

Tools

 * NIF File Format Library and Tools
 * Tools github

Sample files

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

Links

 * Gamebryo (Wikipedia)