| .KMF | Open Source | Pliki z danymi | Kwalitan Memo File | Kwalitan | Open Source |
| .KMO | Unknown Developer | Pliki z danymi | Commercial Bank Czech Financial Data Exchange Format | Unknown Software | Unknown Developer |
| .KMS | Correlate | Pliki z danymi | Correlate Solutions File | Correlate | Correlate Client |
| .KMY | Open Source | Pliki z danymi | KMyMoney Data File | KMyMoney | Open Source |
| .KMZ | Google | Pliki z danymi | Google Earth Placemark File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .KNB | Unknown Developer | Pliki z danymi | Neuro-Expert System Knowledge Base Data File | Neuro-Expert System | Unknown Developer |
| .KND | NEPLAN AG | Pliki z danymi | NEPLAN-DOS Import Or Export File | NEPLAN Electricity | NEPLAN AG |
| .KNF | Orchida Soft | Pliki z danymi | Orchida Knitting System Data | Orchida Knitting System | Orchida Soft |
| .KNO | EvREsearch LTD. | Pliki z danymi | DigIN Serialized Break Model | DigIN | EvREsearch LTD. |
| .KOC | Open Source | Pliki z danymi | Koha Offline Circulation Data | Koha | Open Source |
| .KOK | Recisio | Pliki z danymi | KaraFun Karaoke Data | KaraFun | Recisio |
| .KOS | South-Western Educational Publishing | Pliki z danymi | MicroType Pro Document File | MicroType Pro | South-Western Educational Publishing |
| .KPF | ActiveState | Pliki z danymi | Komodo Project File | ActiveState Komodo IDE | ActiveState |
| .KPP | Software MacKiev | Pliki z danymi | Kid Pix Presentation | Kid Pix | Software MacKiev |
| .KPR | Open Source | Pliki z danymi | KPresenter Presentation | KOffice | Open Source |
| .KPX | Software MacKiev | Pliki z danymi | Kid Pix Picture | Kid Pix | Software MacKiev |
| .KRB | SourceForge | Pliki z danymi | Pyke Knowledge Rule Base | Pyke | SourceForge |
| .KRC | Kra-Tronic Corporation | Pliki z danymi | Mouse And Key Recorder Macro File | Kra-Tronic Corporation Mouse and Key Recorder | Kra-Tronic Corporation |
| .KRF | SPARTA, Inc. | Pliki z danymi | DNSSEC-Tools Keyrec Data File | DNSSEC-Tools | SPARTA, Inc. |
| .KSA | Kubotek Corporation | Pliki z danymi | KeyCreator Settings Archive File | Kubotek USA KeyCreator | Kubotek Corporation |
| .KSM | Pfaff | Pliki z danymi | Pfaff Embroidery Design File Format | Embroidermodder 2 | Open Source |
| .KSP | Luxion | Pliki z danymi | Keyshot Package | Keyshot | Luxion |
| .KSW | Cosmic Patterns Software | Pliki z danymi | Kepler Workflow Document | Kepler | Cosmic Patterns Software |
| .KTE | Open Source | Pliki z danymi | Kite Design File | FoilMaker | Open Source |
| .KTH | Apple | Pliki z danymi | iWork Keynote Theme | Apple Keynote | Apple |
| .KTI | Kelvin TOP-SET | Pliki z danymi | Kelvin TOP-SET Investigator Data | Kelvin TOP-SET Investigator | Kelvin TOP-SET |
| .KTX | Open Source | Pliki z danymi | Kwalitan Data File | Kwalitan | Open Source |
| .KU | Open Source | Pliki z danymi | Knowledge Explorer Knowledge Representation Knowledge Unit | my Knowledge Explorer | Open Source |
| .KUF | K.Y.N.G | Pliki z danymi | K.Y.N.G Update Data | K.Y.N.G | K.Y.N.G |
| .KUU | K.Y.N.G | Pliki z danymi | K.Y.N.G Data File | K.Y.N.G | K.Y.N.G |
| .KVB | MSR Enterprises | Pliki z danymi | Klick-N-View Business Cards | Klick-N-View Business Cards | MSR Enterprises |
| .KVC | Open Source | Pliki z danymi | KVC | KVIrc | Open Source |
| .KW3 | Pacific Software Publishing, Inc. | Pliki z danymi | KanjiWORD Document File | KanjiWORD | Pacific Software Publishing, Inc. |
| .KWB | Open Source | Pliki z danymi | Kwalitan Work File | Kwalitan | Open Source |
| .KWL | KDE | Pliki z danymi | KWalletManager File | KWalletManager | KDE |
| .KWO | KeyWallet GbR | Pliki z danymi | KeyWallet Encrypted Password Storage | KeyWallet | KeyWallet GbR |
| .KWZ | Nintendo | Pliki z danymi | Flipnote Studio 3D Flipnote Data | Flipnote Studio 3D | Nintendo |
| .KXP | SoftKey | Pliki z danymi | KEY Home Gourmet Data | KEY Home Gourmet | SoftKey |
| .KY | Sage | Pliki z danymi | Peachtext List Manager File | Peachtext | Sage |
| .KYN | ESTsoft | Pliki z danymi | ALSee Thumbnail Cache | ALSee | ESTsoft |
| .KZB | Rightware | Pliki z danymi | Kanzi Studio Binary Data | Kanzi Studio | Rightware |
| .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 |
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