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