File extensions starting with the letter N...

  .N64  Nintento 64® Emulation ROM Image
  .NAD  Noder File (Polish)
  .NAN  Nanoscope File
  .NAP  NAP Metafile Vector Image
  .NAV  MSN Application Extension
  .NB   Nota Bene Text File
  .NCB  MS Developer Studio File
  .NCD  Norton Change Directory
  .NCF  Netware Command File
        Lotus Notes Internal Clipboard
  .NDL  Lotus Notes
  .NDO  3D Low-polygon Modeler  
  .NDX  Index (usually dBase compatible)
  .NED  MSN Application Extension
  .NET  Network Configuration
        OrCad Netlist Output File
  .NEW  New Information (e.g., WHATS.NEW)
  .NFF  Image File
        Neutral File Format
  .NFO  Folio Infobase
        Text File [Open in text editor]
        Warez Group Info File
  .NG   Norton Guide Online Documentation
  .NHF  Nero HFS-CD Compilation
  .NIL  Norton Icon Library File
  .NJX  NJStar Document
  .NLB  Oracle 7 Data
  .NLM  Netware Loadable Module
  .NLS  Code Page National Language Support
  .NLU  Norton Live Update E-Mail Trigger File
  .NMS  Numega Softice's Loader File (includes debugging info)
  .NOD  Noder File (Polish)
  .NOL  Nokia Operator Logo
  .NOT  Notes
  .NOW  Text File (e.g., README.NOW)
  .NPD  Noder File (Polish)
  .NPM  Nokia Picture Message
  .NRA  Nero Audio-CD Compilation
  .NRB  Nero CD-ROM Boot Compilation
  .NRG  Norton Registration Entries
        Nero CD-Image
        IsoBuster File
  .NRH  Nero Hybrid CD-ROM Compilation
  .NRI  Nero ISO CD-ROM Compilation
  .NRM  Nero Mixed-Mode-CD Compilation
  .NRT  Nokia RingTone
  .NRU  Nero UDF/ISO CD-ROM Compilation
  .NRV  Nero Video-CD Compilation
  .NS2  Lotus Notes 2 Database
  .NS3  Lotus Notes
  .NS4  Lotus Notes Database
  .NSC  Noder File (Polish)
  .NSF  Lotus Notes Database
  .NSG  Lotus Notes
  .NSH  Lotus Notes
  .NST  Audio File
        Noise Tracker Music Module
  .NSX  HiPer-Six Index File
  .NTF  Lotus Notes Database Template
  .NTS  Norton Tutorial
  .NTX  Clipper Index
  .NUF  Procomm Plus New User Message
  .NW   NoteWorthy 2 File
  .NWC  Noteworthy Composer Song File
  .NWS  MS Outlook Express News File