| .KERNEL | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .KEU | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .KFW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KIK | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .KIL | Unknown Developer | Uncommon Files | Interview File | Unknown Software | Unknown Developer |
| .KKA | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .KKB | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .KLA | Unknown Developer | Ficheiros de Dados | KLARFF Map Data | Unknown Software | Unknown Developer |
| .KLI | Unknown Developer | Ficheiros de Dados | KalKulator Linear Algebra Data | Unknown Software | Unknown Developer |
| .KMO | Unknown Developer | Ficheiros de Dados | Commercial Bank Czech Financial Data Exchange Format | Unknown Software | Unknown Developer |
| .KNS | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .KOD | Unknown Developer | Uncommon Files | Code File | Unknown Software | Unknown Developer |
| .KOSIMA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KOZ | Chaoticom | Ficheiros de Áudio | Audiokoz Music File | Unknown Software | Unknown Developer |
| .KPC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KPK | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KPM | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KPS | Tavultesoft | Ficheiros de Desenvolvedor | Keyman Developer Package Source File | Unknown Software | Unknown Developer |
| .KRM | Kenwood Corporation | Ficheiros de Sistema | Kenwood Firmware Data | Unknown Software | Unknown Developer |
| .KRY | Herolab | Uncommon Files | Herolab Krypten | Unknown Software | Unknown Developer |
| .KSO | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KWG | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KWR | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .KXM | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .KZY | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .L64 | Commodore International | Ficheiros de Configurações | 64LAN Image File | Unknown Software | Unknown Developer |
| .LARGE | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LASXML | Unknown Developer | Ficheiros de Dados | Laser App Data Exchange | Unknown Software | Unknown Developer |
| .LAUNCHER | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LBB | Unknown Developer | Uncommon Files | Liberty Bible DataBase File | Unknown Software | Unknown Developer |
| .LDH | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .LDN | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .LDS | GNU Project | Ficheiros de Desenvolvedor | Binutils LD Linker Script | Unknown Software | Unknown Developer |
| .LEA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .LED | Sony | Ficheiros de Configurações | Sony AIBO LED Lights Control Data | Unknown Software | Unknown Developer |
| .LES | David A. Wheeler | Ficheiros de Dados | Lesson File | Unknown Software | Unknown Developer |
| .LEXT | Olympus Corporation | Ficheiros de Dados | Olympus Lext Measurement Export | Unknown Software | Unknown Developer |
| .LG | Unknown Developer | Ficheiros Compactados | Arhangel Compressed Archive | Unknown Software | Unknown Developer |
| .LGF | Microsoft Corporation | Ficheiros de Dados | Microsoft Windows Application Log File | Unknown Software | Unknown Developer |
| .LIB | Various Developers | Ficheiros de Dados | Generic Data Library | Unknown Software | Unknown Developer |
| .LIM | Unknown Developer | Ficheiros Compactados | Limit Compressed Data | Unknown Software | Unknown Developer |
| .LISTING | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LIZ | Unknown Developer | Ficheiros Compactados | Compressed List File | Unknown Software | Unknown Developer |
| .LI_ | Unknown Developer | Uncommon Files | Rukus File | Unknown Software | Unknown Developer |
| .LKH | Unknown Developer | Uncommon Files | Worm.Generic.LKH Virus File | Unknown Software | Unknown Developer |
| .LKU | STMicroelectronics | Ficheiros Executáveis | ST Microelectronics Linked Unit Data | Unknown Software | Unknown Developer |
| .LNV | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .LOAD | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LOADER | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LOAN | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LOGO | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LOJ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .LOW | Digital Equipment Corporation | Ficheiros de Sistema | PDP-10 Low Segment Of A Two-segment Program | Unknown Software | Unknown Developer |
| .LP1 | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .LPI | Unknown Developer | Ficheiros de Dados | Laser Printer Information | Unknown Software | Unknown Developer |
| .LPS | DAZ 3D | Ficheiros de Imagem 3D | Bryce Leaf Shape File | Unknown Software | Unknown Developer |
| .LQC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .LSW | Technics | Ficheiros de Configurações | Technics Keyboard Current Panel File | Unknown Software | Unknown Developer |
| .LU | ThoughtWing, LLC | Uncommon Files | ThoughtWing Library Unit File | Unknown Software | Unknown Developer |
| .LVH | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .LVX | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .LYB | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .LYZ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .LZW | Unknown Developer | Ficheiros Compactados | LZW Compressed Archive File | Unknown Software | Unknown Developer |
| .LZZZZZZZ | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .M3K | Unknown Developer | Ficheiros Compactados | Interactive Digital Content File | Unknown Software | Unknown Developer |
| .M5D | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .M9D | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .MAC2 | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MACRO | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MAILBOX | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MAPS | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MARIO | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MAU | Unknown Developer | Uncommon Files | Media Attachment Unit | Unknown Software | Unknown Developer |
| .MCH | Interscape | Ficheiros de Configurações | Machinery HDR Effects | Unknown Software | Unknown Developer |
| .MCV | Visicom Media Inc | Ficheiros de Configurações | ManyCam Effect File | Unknown Software | Unknown Developer |
| .MC_ | Unknown Developer | Ficheiros Compactados | Musicato Compressed File | Unknown Software | Unknown Developer |
| .MD_ | Unknown Developer | Ficheiros de Configurações | Visc15 Adressen Setup File | Unknown Software | Unknown Developer |
| .ME | Unknown Developer | Uncommon Files | Temporary Delete Me File | Unknown Software | Unknown Developer |
| .ME1 | Unknown Developer | Ficheiros de Dados | 21 Sample Winexam File | Unknown Software | Unknown Developer |
| .ME2 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .MEI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .MEK | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .MEMORY | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MERLIN | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MESSAGES | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .METAL | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MFC | Unknown Developer | Uncommon Files | Mankind File | Unknown Software | Unknown Developer |
| .MFO | Perl Express Group | Ficheiros de Dados | Perl ModInfo Descriptor File | Unknown Software | Unknown Developer |
| .MHW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .MICE | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MISC | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MJM | Unknown Developer | Ficheiros de Dados | JDF Data Exchange Format | Unknown Software | Unknown Developer |
| .MK8 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .MLI | Unknown Developer | Ficheiros de Dados | Encyclopedia Media List | Unknown Software | Unknown Developer |
| .MLTV | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MMV | Sony | Ficheiros de Vídeo | MicroMV Video File | Unknown Software | Unknown Developer |
| .MNW | Unknown Developer | Uncommon Files | Menu File | Unknown Software | Unknown Developer |
| .MODEM | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .MOJ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
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