| .TXK | Unknown Developer | Fichiers textes | Karaoke Song Lyrics | KaraDOS | Unknown Developer |
| .TXM | CFP Software Limited | Fichiers de données | CFPwinMan Document File | Unknown Software | Unknown Developer |
| .TXW | Yamaha Corporation | Fichiers audio | Yamaha TX16W Audio File | TX16WConverter | Unknown Developer |
| .TY2 | Unknown Developer | Fichiers divers | Gualtieri Theme Maker File | Gualtieri Theme Maker | Unknown Developer |
| .TYP | Unknown Developer | Fichiers divers | Thumbs32 File | Unknown Software | Unknown Developer |
| .TZG | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .U2C | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .U2E | Unreal Software | Fichiers divers | Unreal Game Translation | Unknown Software | Unknown Developer |
| .U4A | Unknown Developer | Fichiers exécutables | UnInstaller Archive File | Unknown Software | Unknown Developer |
| .U8 | Nintendo | Fichiers de jeu | Mario Kart Wii Archive File | Unknown Software | Unknown Developer |
| .UAD | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .UAP | Siemens AG | Fichiers compressés | SIMATIC WinCC User Archive Export | Unknown Software | Unknown Developer |
| .UB1 | Unknown Developer | Fichiers vidéo | X-Driven DRS-1100 Recorded Video | Unknown Software | Unknown Developer |
| .UBF | Marker Communication | Fichiers de données | MXT3010 Universal Boot Format | Unknown Software | Unknown Developer |
| .UBI | Ubisoft | Fichiers de jeu | Ubisoft Logo Animation | Unknown Software | Unknown Developer |
| .UBZ | Unknown Developer | Fichiers de données | Open-Sankore Document | Open-Sankoré | Unknown Developer |
| .UC2 | Nico De Vries | Fichiers compressés | UltraCompressor 2 Archive | AIPNL UltraCompressor 2.3 or UltraExpander | Unknown Developer |
| .UCA | Unknown Developer | Fichiers divers | Unicode Collation Algorithm Data File | Unknown Software | Unknown Developer |
| .UCI | SysDevSoftware | Fichiers de sauvegarde | UFS Explorer Backup File | Unknown Software | Unknown Developer |
| .UK_ | Unknown Developer | Fichiers divers | Mcguiness File | Unknown Software | Unknown Developer |
| .UND | DHI | Fichiers de données | MOUSE Urban Network Datafile | Unknown Software | Unknown Developer |
| .UNIX BAR COMPRESSED FILE ARCHIVE | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .UNKNOWN | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .UNM | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .UP | Apple | Fichiers de données | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .UPD | Various Developers | Fichiers textes | Program Update Information | Unknown Software | Unknown Developer |
| .UPDATED | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .UTB | Unknown Developer | Fichiers de sauvegarde | µTBackup Backup | µTBackup | Unknown Developer |
| .UVC | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .UVZ | Unknown Developer | Fichiers compressés | DECE ZIP Compressed Data | Unknown Software | Unknown Developer |
| .UXR | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .V2Q | Texas Instruments, Inc. | Fichiers de données | TI Voyage 200 Certificate File | Unknown Software | Unknown Developer |
| .V48 | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .V50 | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VAD | Blue Marble Geographics | Fichiers de données | Mapper Variant | Unknown Software | Unknown Developer |
| .VAR | M:Pact Technologies | Fichiers de développeurs | Variable Data | Icon Author | Unknown Developer |
| .VAX | Unknown Developer | Fichiers divers | Pbm Plus File | Unknown Software | Unknown Developer |
| .VCMP | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VCY | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VC_ | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VDH | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VDMPVF | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VDO | Unknown Developer | Fichiers exécutables | Heathen Virus File | Unknown Software | Unknown Developer |
| .VEX | Unknown Developer | Fichiers de données | VLBI Experiment Definition Data | Very Long Baseline Interferometry (VLBI) | Unknown Developer |
| .VFF | Sun Microsystems | Fichiers Raster Image | Sun TAAC Graphic File | Unknown Software | Unknown Developer |
| .VHA | Macromedia | Fichiers divers | Macromedia Sitespring File | Unknown Software | Unknown Developer |
| .VHDPMEM | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VHP | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VIEWER | Apple | Fichiers de données | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .VI_ | Unknown Developer | Fichiers audio | Samplitude Compressed File | Audio Waveprg | Unknown Developer |
| .VLQ | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VMCZ | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VOICE | Apple | Fichiers de données | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .VOT | Unknown Developer | Fichiers Raw 'appareil photo | Recorded Video File | Unknown Software | Unknown Developer |
| .VPB | Unknown Developer | Fichiers Raster Image | Quantel VPB Image Format | Unknown Software | Unknown Developer |
| .VQE | Yamaha Corporation | Fichiers audio | Yamaha Sound-VQ Locator File | Unknown Software | Unknown Developer |
| .VQL | Yamaha Corporation | Fichiers audio | Yamaha Sound-VQ Locator File | Unknown Software | Unknown Developer |
| .VRA | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VSR | Microsoft Corporation | Fichiers de base de données | Microsoft Access Report | Unknown Software | Unknown Developer |
| .VT | Unknown Developer | Fichiers de données | VT100 Terminal Data File | Unknown Software | Unknown Developer |
| .VUX | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .VVR | Unknown Developer | Fichiers de données | ViVerify Repair File | ViVerify Repair | Unknown Developer |
| .VXX | Unknown Developer | Fichiers système | IOsubsys | Unknown Software | Unknown Developer |
| .VYB | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .W2F | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .W73 | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .WC4 | Unknown Developer | Fichiers divers | WinCheckIt4 Settings File | Unknown Software | Unknown Developer |
| .WEBARCHIV | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .WEI | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .WF2 | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .WINDOWSLIV | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .WINDOWSMED | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .WLF | Microsoft Corporation | Fichiers de données | Microsoft Windows 98/Me Dr. Watson Log | Unknown Software | Unknown Developer |
| .WLO | JinKe Electronic Company | Fichiers eBook | WOLF eBook | Unknown Software | Unknown Developer |
| .WLT | Unknown Developer | Fichiers graphiques | WaveL Wavelet Compressed Graphic | Unknown Software | Unknown Developer |
| .WM5 | Unknown Developer | Fichiers divers | Dyndlg2 File | Dyndlg2 | Unknown Developer |
| .WMH | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .WMO | World Meteorological Organization | Fichiers de données | WMO Binary Format File | Unknown Software | Unknown Developer |
| .WSQ | UTAU Team | Fichiers audio | UTAU File | Unknown Software | Unknown Developer |
| .WS_ | Unknown Developer | Fichiers de paramètres | Visc15 Adressen Setup File | Unknown Software | Unknown Developer |
| .WVT | Unknown Developer | Fichiers de données | Compuwx Export Data | Unknown Software | Unknown Developer |
| .WWZ | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .WXW | WiNRADiO | Fichiers divers | WiNRADiO Extended Wave File | Unknown Software | Unknown Developer |
| .X23 | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X2M | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X33 | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X3M | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XACT | XactSystems | Fichiers divers | XactScript File | Unknown Software | Unknown Developer |
| .XAD | Riven the Mage | Fichiers audio | eXotic ADlib Sound Format File | Unknown Software | Unknown Developer |
| .XAK | Unknown Developer | Fichiers divers | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XB~ | Unknown Developer | Fichiers divers | IC File | Unknown Software | Unknown Developer |
| .XCK | Unknown Developer | Fichiers de données | Extended Crack File | Unknown Software | Unknown Developer |
| .XD | Unknown Developer | Fichiers de données | CCS-lib.2 Examples Motif-CC File | Unknown Software | Unknown Developer |
| .XDE | Unknown Developer | Fichiers 3D | Tgif-3.0 File | Unknown Software | Unknown Developer |
| .XDSL | D-Link Corporation | Fichiers système | D-link Router UK Firmware Update File | Unknown Software | Unknown Developer |
| .XED | Unknown Developer | Fichiers de données | XED Chemical Modeler Input/Output Data | Unknown Software | Unknown Developer |
| .XI1 | Unknown Developer | Fichiers divers | Unknown File Type | Unknown Software | Unknown Developer |
| .XLTD | Unknown Developer | Fichiers divers | Thunder Temporary Data File | Unknown Software | Unknown Developer |
| .XMAS | Apple | Fichiers de données | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .XMIT | IBM | Fichiers de données | IBM XMIT Data | Unknown Software | Unknown Developer |
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