| .L4D | MAXON Computer | Indstillingsfiler | Cinema 4D Layout File | MAXON Cinema 4D | MAXON Computer |
| .L64 | Commodore International | Indstillingsfiler | 64LAN Image File | Unknown Software | Unknown Developer |
| .LANG | Mojang | Indstillingsfiler | Minecraft Language File | Microsoft Notepad | Microsoft Corporation |
| .LAUNCH | Rogue Wave | Indstillingsfiler | Zend Studio Debugger Configuration Data | Eclipse IDE for Java Developers | The Eclipse Foundation |
| .LAY | Tecplot, Inc | Indstillingsfiler | Tecplot Layout File | Tecplot 360 | Tecplot, Inc |
| .LAYOUT | Apple | Indstillingsfiler | Apple MainStage Layout Data | Logic Studio | Apple |
| .LBU | Interscape | Indstillingsfiler | Cloaked Affiliate Link Builder Settings File | Cloaked Affiliate Link Builder | Interscape |
| .LCC | IBM | Indstillingsfiler | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .LED | Sony | Indstillingsfiler | Sony AIBO LED Lights Control Data | Unknown Software | Unknown Developer |
| .LENS | Autodesk, Inc. | Indstillingsfiler | Autodesk Stitcher Camera Profile | Autodesk Stitcher Unlimited | Autodesk, Inc. |
| .LES | David A. Wheeler | Indstillingsfiler | Lesson File | Mklesson | David A. Wheeler |
| .LF | Concept Software | Indstillingsfiler | SoftwareKey License | Protection PLUS | Concept Software |
| .LGT | Microsoft Corporation | Indstillingsfiler | Let's Go! Theme File | Let's Go! | Microsoft Corporation |
| .LH3D | BeLight Software | Indstillingsfiler | Live Home 3D Project | Live Home 3D | BeLight Software |
| .LIC | Unknown Developer | Indstillingsfiler | Software License File | Microsoft Visual C++ | Microsoft Corporation |
| .LIR | Applied Digital | Indstillingsfiler | ADI Ocelot Settings File | C-Max | Applied Digital |
| .LKF | PCS Systemtechnik GmbH | Indstillingsfiler | INTUS Terminal Keyboard Settings | INTUS 5600 MULTIFUNCTIONAL TERMINAL | PCS Systemtechnik GmbH |
| .LKG | Hewlett-Packard | Indstillingsfiler | HP-UX Configuration Data | HP-UX 11i Web Server Suite | Hewlett-Packard |
| .LLC | LapLink Software | Indstillingsfiler | LapLink Saved Connection File | LapLink | LapLink Software |
| .LLP | General Electric Company | Indstillingsfiler | VersaPro Local Logic Block | VersaPro | General Electric Company |
| .LOCAL | Embarcadero Technologies | Indstillingsfiler | Delphi User-Specific Project Options | Delphi (IDE) | Embarcadero Technologies |
| .LOOK | Adobe Systems Incorporated | Indstillingsfiler | SpeedGrade Look File | Adobe SpeedGrade | Adobe Systems Incorporated |
| .LOP | ValuSoft | Indstillingsfiler | MasterCook Layout File | ValuSoft MasterCook | ValuSoft |
| .LSV | Light-O-Rama | Indstillingsfiler | Light-O-Rama Sequence Editor Visual Preference File | Light-O-Rama | Light-O-Rama |
| .LSW | Technics | Indstillingsfiler | Technics Keyboard Current Panel File | Unknown Software | Unknown Developer |
| .LT | Andrew Jewett | Indstillingsfiler | Moltemplate Data File | Moltemplate | Andrew Jewett |
| .LVA | Logitech | Indstillingsfiler | Logitech Video Effects Avatar File | Logitech Webcam Software | Logitech |
| .LVF | Logitech | Indstillingsfiler | Logitech Video Effects File | Logitech Webcam Software | Logitech |
| .LVT | Open Source | Indstillingsfiler | Land Surface Verification Toolkit Configuration | Land Information System Verification Toolkit (LVT) | Open Source |
| .LWL | Johm Mackernon Software | Indstillingsfiler | Lightwright Printed Paperwork Formatting Instructions Data | LightWright | Johm Mackernon Software |
| .LX | IBM | Indstillingsfiler | LPEX Customization Command Profile File | LPX Editor | IBM |
| .LYT | Adminsoft | Indstillingsfiler | Adminsoft Document Layout File | Adminsoft | Adminsoft |
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