NSF (Nintendo Sound Format, invented by Kevin Horton) is a type of file used to represent NES music, initially developed for storing ripped game music. That means NSF is not a native music format, but a small program that plays the music using the NES's CPU in a slightly similar hardware architecture.
Dn-FamiTracker compresses and compiles the module data and attaches a player program when exporing the NSF file.

To export NSF files, select Create NSF from the File menu to open the NSF export window.
The NSF file options contains some options related to the NSF file format: the song information fields is the same as in the control panel.
There is also a system type option: NTSC, PAL or Dual. Select Dual if you want the NSF to be playable on both NTSC and PAL systems.
The Add. data checkbox indicates generating supporting assembly code to be used with ASM or BIN export when compiling an NSF file from source.

A few other formats beside NSF are also available:

• NSF
  Creates an NSF file.
  
  
• NSFe
  Creates an NSFe file with extra metadata for track labels, track times, and comments.
  
  
• NSF2
  Creates an NSF-compatible file containing NSFe metadata. This metadata is safely ignored in older NSF players.
  
  
• NES
  Encapsulates an NSF into an NROM NES file that can be played in emulators or with flash carts like PowerPaks and Everdrives.
  Note that only non-expansion audio, non-bankswitching modules whose total data is smaller than 32KB are supported.
  
  
• BIN
  Stores only the music data and DPCM samples in separate files for use with NSF driver sources.
  
  
• PRG
  Creates a single 32 kB program ROM file, ready to be used with a NROM-compatible cart for playback on NES hardware.
  Note that only non-expansion audio, non-bankswitching modules whose total data is smaller than 32KB are supported.
  
  
• ASM
  Stores the music data and samples in CA65 assembly format that can be used with driver sources.
  

As of Dn-FT version 0.5.0.2, the export plugin system has been disabled due to a potential security attack vector.
In previous versions until vanilla 0.3.5, an export plugin system was added that allows exporting to custom formats. New export targets would appear in the drop-down menu when export plugin DLLs were added.