| .ITX | IBM | Fichiers textes | ITX Form Template | FileNet eForms | IBM |
| .IVP | Oracle Corporation | Fichiers textes | Panorama File | Java | Oracle Corporation |
| .IWP | Incomedia | Fichiers textes | Website X5 Project | Website X5 | Incomedia |
| .IX | Corel | Fichiers textes | Corel WordPerfect Office Template File | Corel WordPerfect | Corel |
| .IXT | Image Solutions, Inc. | Fichiers textes | ISIPublisher Publication Template | ISIPublisher | Image Solutions, Inc. |
| .JHD | PVR Narasimha Rao | Fichiers textes | Jagannatha Hora Document | Jagannatha Hora | PVR Narasimha Rao |
| .JIS | Glenn Rosenthal | Fichiers textes | Japanese Industry Standard Text | JWPce | Glenn Rosenthal |
| .JOT | King Stairs | Fichiers textes | Jot+ Notes Note Data | Jot+ Notes | King Stairs |
| .JPR | Microsoft Corporation | Fichiers textes | WordPad Document | Microsoft WordPad | Microsoft Corporation |
| .JSD | Jazer Solutions | Fichiers textes | Jazer Data File | Jazer | Jazer Solutions |
| .JSW | JustSystems | Fichiers textes | Ichitaro 4.0 Document | Ichitaro | JustSystems |
| .JTD | JustSystems | Fichiers textes | Ichitaro Document | Ichitaro | JustSystems |
| .JWRT | Benoit Widemann | Fichiers textes | JoliWrite Data File | JoliWrite | Benoit Widemann |
| .KDF | Kinko's | Fichiers textes | Kinko's File Prep Tool Data | Kinko's File Prep Tool | Kinko's |
| .KES | Kurzweil Education | Fichiers textes | Kurzweil 3000 Document | Kurzweil 3000 | Kurzweil Education |
| .KNT | SourceForge | Fichiers textes | KeyNote Note File | Keynote | SourceForge |
| .KON | Yahoo! | Fichiers textes | Yahoo! Widget XML File | Yahoo! Widgets | Yahoo! |
| .KPT | Open Source | Fichiers textes | KPresenter Template File | KOffice | Open Source |
| .KTF | Microsoft Corporation | Fichiers textes | Microsoft Dynamics AX Kernel Text Data | Microsoft Dynamics AX | Microsoft Corporation |
| .KWD | KDE | Fichiers textes | KWord Document | KOffice | Open Source |
| .LAX | AnetSoft | Fichiers textes | AnetHelpTool JavaHelp Viewer Data | AnetHelpTool | AnetSoft |
| .LBL | Interscape | Fichiers textes | Now Contact Label Template | Now Up-to-Date (Now Contact) | Now Software |
| .LBT | Microsoft Corporation | Fichiers textes | FoxPro Label Memo | Microsoft Visual FoxPro | Microsoft Corporation |
| .LDI | Trudi Ersvaer (co-developer) | Fichiers textes | LDIF File | Apache Directory Server/Studio | Apache Software Foundation |
| .LEF | Sublime HQ Pty Ltd | Fichiers textes | Lenex XML Data | Sublime Text | Sublime HQ Pty Ltd |
| .LET | Genesis 2000, Inc | Fichiers textes | Genesis 2000 Data | Genesis 2000 | Genesis 2000, Inc |
| .LGN | Microsoft Corporation | Fichiers textes | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LHD | Unknown Developer | Fichiers textes | Label Home Document File | Label Home | Unknown Developer |
| .LIB | Various Developers | Fichiers textes | Generic Data Library | Unknown Software | Unknown Developer |
| .LIS | SourceForge | Fichiers textes | SQR (Structured Query Reporting) Output File | Microsoft Notepad | Microsoft Corporation |
| .LNT | Gimpel Software | Fichiers textes | PC-lint/FlexeLint Configuration File | Microsoft Notepad | Microsoft Corporation |
| .LOG | Unknown Developer | Fichiers textes | Log File | Microsoft Notepad | Microsoft Corporation |
| .LSP | Open Source | Fichiers textes | Lisp Program Source Code File | MacroMates TextMate | MacroMates |
| .LST | Unknown Developer | Fichiers textes | Data List | LibreOffice | The Document Foundation |
| .LTR | Sublime HQ Pty Ltd | Fichiers textes | Letter Document | Microsoft Notepad | Microsoft Corporation |
| .LTX | GSC Game World | Fichiers textes | S.T.A.L.K.E.R. Properties File | GSC Game World S.T.A.L.K.E.R.: Call of Pripyat | GSC Game World |
| .LUF | Santanu Ghosh | Fichiers textes | Lipikar Uniform Format File | Lipikar | Santanu Ghosh |
| .LWD | EditShare | Fichiers textes | Lightworks Data File | Lightworks | EditShare |
| .LWP | IBM | Fichiers textes | Lotus Word Pro Document | IBM Lotus Word Pro | IBM |
| .LXFML | The LEGO Group | Fichiers textes | LEGO Digital Designer XML File | LEGO Digital Designer | The LEGO Group |
| .LYT | Adminsoft | Fichiers textes | Adminsoft Document Layout File | Adminsoft | Adminsoft |
| .LYX | Open Source | Fichiers textes | XWE File | XWE | Open Source |
| .M15 | Moving Picture Experts Group | Fichiers textes | MPEG Video File | CyberLink PowerDVD | CyberLink |
| .MACWRITE | Apple | Fichiers textes | MacWrite Text Document | MacWrite | Apple |
| .MAGNET | Vuze Inc. | Fichiers textes | Magnet Link Text File | BitTorrent | BitTorrent |
| .MAN | Unknown Developer | Fichiers textes | Unix Manual | LibreOffice | The Document Foundation |
| .MANIFEST | Microsoft Corporation | Fichiers textes | Windows Application Manifest File | Microsoft Notepad | Microsoft Corporation |
| .MAP | id Software | Fichiers textes | Quake Engine Map File | Valve Hammer Editor | Valve |
| .MDH | Balendu Sharma Dadhich | Fichiers textes | Madhyam Document | Madhyam | Balendu Sharma Dadhich |
| .MDK | Microsoft Corporation | Fichiers textes | Madoko Document File | Madoko | Microsoft Corporation |
| .MDOWN | John Gruber | Fichiers textes | Markdown Markup Language Source Code | Microsoft Notepad | Microsoft Corporation |
| .ME | Unknown Developer | Fichiers textes | Temporary Delete Me File | Unknown Software | Unknown Developer |
| .MELL | Mellel | Fichiers textes | Mellel Word Processing File | Mellel | Mellel |
| .META4 | JDownloader Team | Fichiers textes | Metalink 4.0 Data | Free Download Manager | Free Download Manager.ORG |
| .MIN | Okuma | Fichiers textes | Okuma CNC Program File | Microsoft Notepad | Microsoft Corporation |
| .MKD | Malz++Kassner | Fichiers textes | CAD 6 Drawing File | CAD6 Studio | Malz++Kassner |
| .MM4 | Microsoft Corporation | Fichiers textes | Microsoft Windows Word Processing Format | Microsoft Windows | Microsoft Corporation |
| .MMO | Memory-Map | Fichiers textes | Memory Map Overlay File | Memory-Map Navigator | Memory-Map |
| .MNL | Autodesk, Inc. | Fichiers textes | AutoCAD Menu LISP File | Autodesk AutoCAD | Autodesk, Inc. |
| .MNT | Microsoft Corporation | Fichiers textes | FoxPro Menu Memo | Microsoft Visual FoxPro | Microsoft Corporation |
| .MPL | Sony | Fichiers textes | AVCHD Playlist File | CyberLink PowerDVD | CyberLink |
| .MPR | Open Source | Fichiers textes | Bibexcel Data | BibExcel | Open Source |
| .MPV | Moving Picture Experts Group | Fichiers textes | MPEG Elementary Stream Video File | CyberLink PowerDVD | CyberLink |
| .MRD | Interscape | Fichiers textes | MathRevolt Infinity Document | Infinity | Interscape |
| .MSG | Microsoft Corporation | Fichiers textes | Saved Email Message | Microsoft Outlook Express | Microsoft Corporation |
| .MSH | Martin Schweiger | Fichiers textes | Orbiter 3D Mesh File | Orbiter | Martin Schweiger |
| .MSW | Corel | Fichiers textes | Painter Color Mixer Swatches File | Corel Painter | Corel |
| .MTX | Yannick Delwiche | Fichiers textes | MadTracker 2 Extension | MadTracker 2 | Yannick Delwiche |
| .MVW | McAfee, Inc. | Fichiers textes | Saber LAN Log File | Saber LAN | McAfee, Inc. |
| .MW | Apple | Fichiers textes | MacWrite Text Document | MacWrite | Apple |
| .MWD | Mariner Software | Fichiers textes | Mariner Write Document | Mariner Write | Mariner Software |
| .MWP | IBM | Fichiers textes | Lotus Word Pro SmartMaster File | IBM Lotus Word Pro | IBM |
| .N1E | OM2 Services LLC | Fichiers textes | OM2 OMALI NENA Encrypted Document Version 1 | OM2 OMALI Professional | OM2 Services LLC |
| .N3 | Sublime HQ Pty Ltd | Fichiers textes | Notation3 Document | Notepad++ | Don Ho |
| .NB | Wolfram Research | Fichiers textes | Mathematica Notebook | Wolfram Research Mathematica | Wolfram Research |
| .NCZ | Netcad | Fichiers textes | Netcad Drawing | Netcad | Netcad |
| .NE2 | OM2 Services LLC | Fichiers textes | OM2 OMALI NENA Document Version 2 | OM2 OMALI Professional | OM2 Services LLC |
| .NFD | Nefsis | Fichiers textes | Nefsis Document | Nefsis | Nefsis |
| .NFO | Microsoft Corporation | Fichiers textes | System Information File | Microsoft System Information | Microsoft Corporation |
| .NLC | Nero AG | Fichiers textes | Nero Linux Compilation File | Nero Linux | Nero AG |
| .NOTE | Failsafe Games | Fichiers textes | Notessimo Composition | Notessimo | Starburst |
| .NOTES | Guyswithtowels | Fichiers textes | Memento Notes File | Memento | Guyswithtowels |
| .NOW | The Document Foundation | Fichiers textes | Readme Text Document File | LibreOffice | The Document Foundation |
| .NPD | Netrosoft Corporation | Fichiers textes | Netrosoft Presentation Document | Netrosoft Office Suite | Netrosoft Corporation |
| .NPL | Nokia | Fichiers textes | Nokia Playlist File | Nokia Multimedia Player | Nokia |
| .NRF | The Neat Company | Fichiers textes | Neat Document Folder File | Neat | The Neat Company |
| .NTG | Mark Milam | Fichiers textes | NTGsim Data | NTGsim | Mark Milam |
| .NWM | Sony | Fichiers textes | Sony NWM Display Screen File | Adobe Photoshop | Adobe Systems Incorporated |
| .NWP | Perion Network Ltd | Fichiers textes | Magentic Wallpaper File | IncrediMail | Perion Network Ltd |
| .OAS | Fujitsu Limited | Fichiers textes | Fujitsu OAS Document File | OASYS Viewer | Fujitsu Limited |
| .OCR | URUWORKS | Fichiers textes | Subtitle Workshop OCR Script | URUWorks Subtitle Workshop | URUWORKS |
| .ODIF | ITU-T (International Telecommunication Union, Telecommunication Standardization Sector) | Fichiers textes | Open Document Interchange Format | Unknown Software | Unknown Developer |
| .ODM | Open Source | Fichiers textes | OpenDocument Master Document | Apache OpenOffice | Apache Software Foundation |
| .ODT | Oracle Corporation | Fichiers textes | OpenDocument Text Document | Apache OpenOffice | Apache Software Foundation |
| .OLI | Olivetti | Fichiers textes | Olivetti Text File | Olitext Plus | Olivetti |
| .OMN | Unknown Developer | Fichiers textes | Omnipotent Collection Data | Unknown Software | Unknown Developer |
| .OPT | LexisNexis | Fichiers textes | Concordance Database File | LexisNexis Concordance | LexisNexis |
| .ORO | The Three-Mode Company | Fichiers textes | 3WayPack T3Rotate Output | 3WayPack | The Three-Mode Company |
| .OSC | OpenStreetMap | Fichiers textes | OpenStreetMap Change File | Merkaartor | Bart Vanhauwaert, Chris Browet, Ladislav Láska, and others |
| .OTT | Apache Software Foundation | Fichiers textes | OpenDocument Document Template | Apache OpenOffice | Apache Software Foundation |
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