| .KCD | Symantec Corporation | Arquivos de dados | Rshiphop.kcd Malware | Kayak | Open Source |
| .KDB | Open Source | Arquivos de banco de dados | KeePass Database File | KeePass Password Safe | Open Source |
| .KDBX | Dominik Reichl | Arquivos de dados | KeePass Password Database | KeePass Password Safe | Open Source |
| .KDEVELOP | Free Software Foundation | Arquivos de desenvolvedor | KDevelop Project Data File | KDevelop | Open Source |
| .KDEVPRJ | Free Software Foundation | Arquivos de desenvolvedor | KDevelop Project File | KDevelop | Open Source |
| .KDS | Knyzhov Dmitry | Arquivos de configuração | KD Player Skin File | gVim | Open Source |
| .KEA | Panasonic Corporation | Arquivos de dados | Panasonic KTS File | KEALib software | Open Source |
| .KEYSTORE | Oracle Corporation | Arquivos codificados | Java Keystore File | KeyStore Explorer | Open Source |
| .KFI | Unknown Developer | Arquivos 3D | 3D Forgastest Editor Data | 3D Object Converter | Open Source |
| .KFX | Amazon | Arquivos eBook | Amazon KF10 eBook File | Calibre | Open Source |
| .KGB | Open Source | Arquivos comprimidos | KGB Archive File | KGB Archiver | Open Source |
| .KHF | Open Source | Arquivos de dados | Kwalitan Data File | Kwalitan | Open Source |
| .KHS | Open Source | Arquivos miscelâneas | Kwalitan History Data File | Kwalitan | Open Source |
| .KIWI | Open Source | Arquivos de dados | KiwiViewer Scene | KiwiViewer | Open Source |
| .KIX | Ruud Van Velsen | Arquivos executáveis | KiXtart Script File | PSPad | Open Source |
| .KMAP | Open Source | Arquivos miscelâneas | LyX Keymap | Lyx | Open Source |
| .KMD | Open Source | Arquivos executáveis | ABSTAT For Windows Batch File | ABstat | Open Source |
| .KMF | Open Source | Arquivos de dados | Kwalitan Memo File | Kwalitan | Open Source |
| .KML | Keyhole Corporation | Arquivos GIS | Keyhole Markup Language File | Blender (With Google Earth Importer Plugin) | Open Source |
| .KMY | Open Source | Arquivos de dados | KMyMoney Data File | KMyMoney | Open Source |
| .KMZ | Google | Arquivos GIS | Google Earth Placemark File | Blender (With Google Earth Importer Plugin) | Open Source |
| .KO | Open Source | Arquivos de sistema | Linux Kernel Module File | Linux | Open Source |
| .KOC | Open Source | Arquivos de dados | Koha Offline Circulation Data | Koha | Open Source |
| .KOR | Epic Games | Arquivos de jogos | Unreal Engine Language Localization | PSPad | Open Source |
| .KPR | Open Source | Arquivos de dados | KPresenter Presentation | KOffice | Open Source |
| .KPT | Open Source | Arquivos de Texto | KPresenter Template File | KOffice | Open Source |
| .KRA | Open Source | Arquivos Gráficos | Krita Image | Krita | Open Source |
| .KRF | SPARTA, Inc. | Arquivos de dados | DNSSEC-Tools Keyrec Data File | KMESS (Kevin's Mesh Efficiency Simulator Software) | Open Source |
| .KS | Debian | Arquivos de sistema | Kickstart File | KeyStore Explorer | Open Source |
| .KSG | Open Source | Arquivos 3D | Kwalitan Segment File | Kwalitan | Open Source |
| .KSH | AT&T Labs | Arquivos executáveis | Unix Korn Shell Script | AbiWord | Open Source |
| .KSM | Pfaff | Arquivos de dados | Pfaff Embroidery Design File Format | Embroidermodder 2 | Open Source |
| .KTE | Open Source | Arquivos de dados | Kite Design File | FoilMaker | Open Source |
| .KTX | Open Source | Arquivos de dados | Kwalitan Data File | Kwalitan | Open Source |
| .KU | Open Source | Arquivos de dados | Knowledge Explorer Knowledge Representation Knowledge Unit | my Knowledge Explorer | Open Source |
| .KVA | Open Source | Arquivos comprimidos | KVIrc Compressed Archive | KVIrc | Open Source |
| .KVC | Open Source | Arquivos de dados | KVC | KVIrc | Open Source |
| .KVS | Open Source | Arquivos de desenvolvedor | KVIrc Script | KVIrc | Open Source |
| .KVT | Open Source | Arquivos de configuração | KVIrc Heme | KVIrc | Open Source |
| .KWB | Open Source | Arquivos de dados | Kwalitan Work File | Kwalitan | Open Source |
| .KWD | KDE | Arquivos de Texto | KWord Document | KOffice | Open Source |
| .KWT | Open Source | Arquivos de configuração | KVIrc Theme | KVIrc | Open Source |
| .L | Johan Bontes | Arquivos de dados | Game Of Life File | ModPlug Player | Open Source |
| .LA | Open Source | Arquivos de áudio | Lossless Audio File | XMMS | Open Source |
| .LAB | Corel | Arquivos de layout de página | WordPerfect Label Definition File | BibExcel | Open Source |
| .LAP | Don Ho | Arquivos miscelâneas | Scheme Source Code | PSPad | Open Source |
| .LAY | Tecplot, Inc | Arquivos de dados | Tecplot Layout File | MAME | Open Source |
| .LAZ | Global Heavy Industries | Arquivos de dados | LiquidApps Project File | LASzip | Open Source |
| .LDF | Microsoft Corporation | Arquivos de dados | SQL Server Transaction Log File | gVim | Open Source |
| .LDS | GNU Project | Arquivos de desenvolvedor | Binutils LD Linker Script | gVim | Open Source |
| .LGL | Open Source | Arquivos de jogos | LeechGet Download List | LeechGet | Open Source |
| .LINUX | Open Source | Arquivos de dados | Linux Data File | Linux | Open Source |
| .LIS | SourceForge | Arquivos de Texto | SQR (Structured Query Reporting) Output File | Notepad2 | Open Source |
| .LIST | Open Source | Arquivos de dados | APT List File | Advanced Package Tool (APT) | Open Source |
| .LIT | Microsoft Corporation | Arquivos eBook | Microsoft Reader eBook File | Calibre | Open Source |
| .LMH | Open Source | Arquivos de dados | Memory Hacking Software Memory File | Memory Hacking Software | Open Source |
| .LMP | id Software | Arquivos de jogos | Quake Engine Lump File | Nazi Zombies Portable | Open Source |
| .LNF | Open Source | Arquivos de dados | Oyoaha Lookandfeel Interface Elements File | oyoaha lookandfeel | Open Source |
| .LNG | Nullsoft | Arquivos de complementos | Winamp Language File | MAME | Open Source |
| .LNGX | Dominik Reichl | Arquivos de dados | KeePaas Language Data | KeePass Password Safe | Open Source |
| .LNK | Microsoft Corporation | Arquivos de sistema | Windows File Shortcut | HxD | Open Source |
| .LNT | Gimpel Software | Arquivos de desenvolvedor | PC-lint/FlexeLint Configuration File | MacVim | Open Source |
| .LNX | Commodore International | Arquivos comprimidos | Commodore 64 Lynx Archive | VICE | Open Source |
| .LOF | Open Source | Arquivos de áudio | Audacity File List | Audacity | Open Source |
| .LOL | Apple | Arquivos de desenvolvedor | LOLCODE Source Code FIle | AbiWord | Open Source |
| .LPI | Unknown Developer | Arquivos de dados | Laser Printer Information | Lazarus IDE | Open Source |
| .LPK | ESRI | Arquivos GIS | ArcGIS Layer Package | Lazarus IDE | Open Source |
| .LPS | DAZ 3D | Arquivos 3D | Bryce Leaf Shape File | Lazarus IDE | Open Source |
| .LPT | Interscape | Arquivos de dados | LogPlot Compiled Boring Log File | TOPS-10 | Open Source |
| .LQF | Open Source | Arquivos de dados | LeechFTP Saved Queue | LeechFTP | Open Source |
| .LRC | Various Developers | Arquivos miscelâneas | Lyrics File | StepMania | Open Source |
| .LRF | Aequus Gaming LTD | Arquivos de jogos | League Of Legends Replay File | Calibre | Open Source |
| .LRS | Open Source | Arquivos eBook | Librie Reader Source File | Calibre | Open Source |
| .LRT | Aequus Gaming LTD | Arquivos de jogos | League Of Legends Replay File | YACC | Open Source |
| .LRV | Konica Minolta | Arquivos de dados | Konica Minolta Data Management Software Stored File | Media Player Classic | Open Source |
| .LRX | Sony | Arquivos eBook | Sony Portable Reader File | Calibre | Open Source |
| .LRZ | Open Source | Arquivos comprimidos | Lrzip Compressed Archive | Lrzip | Open Source |
| .LSP | Open Source | Arquivos de desenvolvedor | Lisp Program Source Code File | Clozure CL | Open Source |
| .LST | Unknown Developer | Arquivos de Texto | Data List | AbiWord | Open Source |
| .LTT | Hewlett-Packard | Arquivos de dados | HP Library And Tape Tools Log | PSPad | Open Source |
| .LTX | GSC Game World | Arquivos de jogos | S.T.A.L.K.E.R. Properties File | TEXnicCenter | Open Source |
| .LUG | Unknown Developer | Arquivos de jogos | Game Data | Dragon UnPACKer | Open Source |
| .LVT | Open Source | Arquivos de configuração | Land Surface Verification Toolkit Configuration | Land Information System Verification Toolkit (LVT) | Open Source |
| .LVZ | Open Source | Arquivos de jogos | Continuum Zone Data Graphics | Subspace Continuum | Open Source |
| .LXK | Open Source | Arquivos de dados | Lexicon Link-up File | COREX | Open Source |
| .LYT | Adminsoft | Arquivos de dados | Adminsoft Document Layout File | AbiWord | Open Source |
| .LYX | Open Source | Arquivos de dados | XWE File | XWE | Open Source |
| .LZM | Open Source | Arquivos comprimidos | Slax Module | Slax | Open Source |
| .LZMA | Igor Pavlov | Arquivos comprimidos | LZMA Compressed File | PeaZip | Open Source |
| .LZO | Open Source | Arquivos comprimidos | LZO Compressed File | lzop | Open Source |
| .LZS | Open Source | Arquivos comprimidos | LARC Compressed File Archive | ZipZag | Open Source |
| .LZX | Open Source | Arquivos comprimidos | Amiga LZX Compressed File | cabextract | Open Source |
| .M | MathWorks | Arquivos de desenvolvedor | MATLAB Source Code File | gVim | Open Source |
| .M15 | Moving Picture Experts Group | Arquivos de vídeo | MPEG Video File | CocoModX | Open Source |
| .M1A | Open Source | Arquivos de áudio | MPEG-1 Audio File | Media Player Classic | Open Source |
| .M1V | Roxio | Arquivos de vídeo | MPEG-1 Video File | Eltima Elmedia Player | Open Source |
| .M2A | Unknown Developer | Arquivos de vídeo | MPEG-1 Layer 2 Audio File | Media Player Classic | Open Source |
| .M2P | Moving Picture Experts Group | Arquivos de vídeo | MPEG-2 Program Stream File | Media Player Classic | Open Source |
| .M2T | Roxio | Arquivos de vídeo | HDV Video File | Squared 5 MPEG Streamclip | Open Source |
| .M3 | Blizzard Entertainment Inc. | Arquivos 3D | Blizzard MDX3 Model File | m3_Viewer | Open Source |
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