| .L | Johan Bontes | Pliki z danymi | Game Of Life File | Life32 | Johan Bontes |
| .L16 | JRiver | Pliki z danymi | JRiver Media Center File | JRiver Media Center | JRiver |
| .L2P | IBM | Pliki z danymi | IBM Voice Type Languages Addword Data | IBM Voice Type | IBM |
| .L5K | Rockwell Automation Inc. | Pliki z danymi | RSLogix 5000 File | Studio 5000 Logix Designer | Rockwell Automation Inc. |
| .L6T | Line 6 | Pliki z danymi | Line 6 Tone File | Line 6 Gearbox | Line 6 |
| .LA | Open Source | Pliki z danymi | Lossless Audio File | Nullsoft Winamp | Nullsoft |
| .LAB | Corel | Pliki z danymi | WordPerfect Label Definition File | Corel WordPerfect | Corel |
| .LABEL | DYMO | Pliki z danymi | DYMO Label File | DYMO Printers | DYMO |
| .LAC | IBM | Pliki z danymi | Cognos Local Authentication Cache | Cognos software | IBM |
| .LAO | Epson US | Pliki z danymi | EPSON SMART PANEL File | EPSON SMART PANEL | Epson US |
| .LAR | Liquid Audio Inc | Pliki z danymi | Liquid Audio Player Registration File Format | Liquid Audio Player | Liquid Audio Inc |
| .LARGE | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .LAS | Various Developers | Pliki z danymi | LIDAR Data Exchange File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .LAST | Valve | Pliki z danymi | Valve Steam Data | Steam | Valve |
| .LASXML | Unknown Developer | Pliki z danymi | Laser App Data Exchange | Unknown Software | Unknown Developer |
| .LAT | Leslie Lamport | Pliki z danymi | LaTeX File | LaTex | Leslie Lamport |
| .LAUNCHER | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .LAV | PSU Miller Lab | Pliki z danymi | DNA Sequence Alignment File | LASTZ | PSU Miller Lab |
| .LAVS | Liquid Audio Inc | Pliki z danymi | Liquid Audio Secured Download File | Liquid Audio Player | Liquid Audio Inc |
| .LAW | E*Law Publishing Limited | Pliki z danymi | eLawForms | eLawForms | E*Law Publishing Limited |
| .LAY | Tecplot, Inc | Pliki z danymi | Tecplot Layout File | Tecplot 360 | Tecplot, Inc |
| .LAZ | Global Heavy Industries | Pliki z danymi | LiquidApps Project File | Liquid Studio | Global Heavy Industries |
| .LA_ | Texas Instruments, Inc. | Pliki z danymi | TI Databook File | TI Connect | Texas Instruments, Inc. |
| .LBA | ShopTalk Systems | Pliki z danymi | Liberty BASIC Source Code | Liberty Basic | ShopTalk Systems |
| .LBD | Llamagraphics | Pliki z danymi | Life Balance User Data File | Life Balance | Llamagraphics |
| .LBE | Llamagraphics | Pliki z danymi | Life Balance Xml-based Exchange Data | Life Balance | Llamagraphics |
| .LBL | Interscape | Pliki z danymi | Now Contact Label Template | Now Up-to-Date (Now Contact) | Now Software |
| .LBM | Electronic Arts | Pliki z danymi | Deluxe Paint Bitmap Image File | Canvas X | ACD Systems |
| .LBP | Schneider Electric | Pliki z danymi | ProWORX Nxt Logic Pointer Data | ProWORX | Schneider Electric |
| .LBR | Dag Agren, Circlesoft | Pliki z danymi | LU Library Archive | The Unarchiver | Dag Agren, Circlesoft |
| .LBX | Microsoft Corporation | Pliki z danymi | FoxPro Label File | Microsoft Visual FoxPro | Microsoft Corporation |
| .LBXLLS | Interscape | Pliki z danymi | Logos Libronix 3.0 Data | Logos Bible Software | Interscape |
| .LBXWKS | Libronix Corporation | Pliki z danymi | Libronix DLS Workspace | Digital Library System | Libronix Corporation |
| .LCC | IBM | Pliki z danymi | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .LCD | ABBYY | Pliki z danymi | ABBYY Language File | ABBYY FineReader | ABBYY |
| .LCN | Microsoft Corporation | Pliki z danymi | License File | Microsoft Windows | Microsoft Corporation |
| .LCP | Mark Finney | Pliki z danymi | FARSITE Landscape Data | FARSITE | Mark Finney |
| .LCS | Swiftpage, Inc. | Pliki z danymi | ACT! History Data | Act! | Swiftpage, Inc. |
| .LCT | Oracle Corporation | Pliki z danymi | Oracle Database Configuration File | Oracle Database | Oracle Corporation |
| .LCX | Cray Inc. | Pliki z danymi | LC Model | Microsoft Notepad | Microsoft Corporation |
| .LD | deltaComm Development Inc | Pliki z danymi | Telix Long Distance Codes Data | Telix for Windows | deltaComm Development Inc |
| .LD2 | Kevin Yau | Pliki z danymi | Lingoes Dictionary File | Lingoes | Kevin Yau |
| .LDF | Microsoft Corporation | Pliki z danymi | SQL Server Transaction Log File | Microsoft SQL Server | Microsoft Corporation |
| .LDIF | Mozilla | Pliki z danymi | LDAP Data Interchange Format File | Mozilla Thunderbird | Mozilla |
| .LDL | Corel Corporation | Pliki z danymi | Corel Paradox Delivered Library File | Corel Paradox | Corel |
| .LDP | Kevin Yau | Pliki z danymi | Lingoes Dictionary File | Lingoes | Kevin Yau |
| .LDS | GNU Project | Pliki z danymi | Binutils LD Linker Script | Microsoft Notepad | Microsoft Corporation |
| .LDT | DIAL | Pliki z danymi | Eulumdat Formatted Luminaire Data File | DIAL DIALux | DIAL |
| .LDX | Global Heavy Industries | Pliki z danymi | Liquid Studio Compiled Executable | Liquid Studio | Global Heavy Industries |
| .LEGAL | DaveTech | Pliki z danymi | DaveTech Legal Document | Notepad++ | Don Ho |
| .LEP | CAM Development | Pliki z danymi | Label and Envelope Designer Plus 2000 Data File | Label and Envelope Designer Plus 2000 | CAM Development |
| .LES | David A. Wheeler | Pliki z danymi | Lesson File | Mklesson | David A. Wheeler |
| .LET | Genesis 2000, Inc | Pliki z danymi | Genesis 2000 Data | Genesis 2000 | Genesis 2000, Inc |
| .LETTER | Proofpoint, Inc. | Pliki z danymi | Undeliverable Mail File | Sendmail | Proofpoint, Inc. |
| .LEV | Interscape | Pliki z danymi | NetHack Level File | NetHack | Interscape |
| .LEX | Adobe Systems Incorporated | Pliki z danymi | Adobe Linguistic Library Data File | Adobe Illustrator CC | Adobe Systems Incorporated |
| .LEXT | Olympus Corporation | Pliki z danymi | Olympus Lext Measurement Export | Unknown Software | Unknown Developer |
| .LF | Concept Software | Pliki z danymi | SoftwareKey License | Protection PLUS | Concept Software |
| .LFB | Laserfiche | Pliki z danymi | Laserfiche Briefcase | Laserfiche Client and Server | Laserfiche |
| .LFM | Interscape | Pliki z danymi | LifeForm Data | Life Form Studio | Interscape |
| .LFP | Ipro Tech | Pliki z danymi | IPRO LFP File | IPRO Tech iConvert | Ipro Tech |
| .LGA | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGB | Intuit, Inc. | Pliki z danymi | QuickBooks Little Green Box | QuickBooks | Intuit, Inc. |
| .LGC | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGD | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGE | Don Ho | Pliki z danymi | Log Data | Microsoft Notepad | Microsoft Corporation |
| .LGF | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGG | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGH | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGI | Softronics Inc. | Pliki z danymi | Multimedia Logic File | MultiMedia Logic | Softronics Inc. |
| .LGJ | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGL | Open Source | Pliki z danymi | LeechGet Download List | LeechGet | Open Source |
| .LGM | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGN | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGP | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGS | Microsoft Corporation | Pliki z danymi | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGU | Microsoft Corporation | Pliki z danymi | LG Windows CE Upgrade Data | Microsoft Windows CE Embedded | Microsoft Corporation |
| .LGV | Microsoft Corporation | Pliki z danymi | Debugging Tools For Windows Logger Log | Debugging Tools for Windows | Microsoft Corporation |
| .LHP | Electric Butterfly, Inc. | Pliki z danymi | Lighthouse Organizer Data | Lighthouse Organizer | Unknown Developer |
| .LHR | Intuit, Inc. | Pliki z danymi | Quicken Financial Life For Mac Financial Data | Quicken Essentials for Mac | Intuit, Inc. |
| .LHX | GridSense | Pliki z danymi | LineTracker Firmware Upgrade | LineMan Remote | GridSense |
| .LIA | Altium | Pliki z danymi | P-CAD Schematics Library | P-CAD | Altium |
| .LIB | Various Developers | Pliki z danymi | Generic Data Library | Unknown Software | Unknown Developer |
| .LICENSE | Unknown Developer | Pliki z danymi | Generic License File | Microsoft Visual Studio | Microsoft Corporation |
| .LIF | The LEGO Group | Pliki z danymi | LEGO Digital Designer Assets File | LEGO Digital Designer | The LEGO Group |
| .LIFE | Light of Creativity, Inc. | Pliki z danymi | Light Notebook File | Light Notebook | Light of Creativity, Inc. |
| .LIN | Autodesk, Inc. | Pliki z danymi | AutoCAD Linetype File | Autodesk AutoCAD | Autodesk, Inc. |
| .LINUX | Open Source | Pliki z danymi | Linux Data File | FreeBSD | The FreeBSD Community |
| .LIST | Open Source | Pliki z danymi | APT List File | Advanced Package Tool (APT) | Open Source |
| .LISTING | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .LIV | Cantoche | Pliki z danymi | Living Actor Actor File | Living Actor | Cantoche |
| .LIVEREG | Symantec Corporation | Pliki z danymi | Symantec Antivirus Session File | Symantec LiveReg | Symantec Corporation |
| .LIVEUPDATE | Symantec Corporation | Pliki z danymi | Symantec LiveUpdate File | Norton SystemWorks | Symantec Corporation |
| .LIX | Interscape | Pliki z danymi | Logos Library System File | Logos Bible Software | Interscape |
| .LK | Revelation Software | Pliki z danymi | Primary Data Storage Space | OpenInsight | Revelation Software |
| .LKB | Faiveley Transport Group | Pliki z danymi | Faiveley Data Recorder File | Bach-Simpson Event Recorders | Faiveley Transport Group |
| .LKO | Microsoft Corporation | Pliki z danymi | Outlook Express Linked Object | Microsoft Outlook Express | Microsoft Corporation |
| .LKP | Microsoft Corporation | Pliki z danymi | Microsoft Systems Management Server (SMS) Data | Microsoft Systems Management Server | Microsoft Corporation |
| .LKR | Microchip Technology Inc. | Pliki z danymi | MPLAB Linker Data | MPLAB C Compiler | Microchip Technology Inc. |
| .LKS | Captel SARL | Pliki z danymi | Offline Liberkey Packages | LiberKey | Captel SARL |
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