| .WEAP | id Software | Arquivos de jogos | Quake 3 Engine Weapon File | AbiWord | Open Source |
| .WEBARCHIVE | Apple | Arquivos Web | Safari Web Archive | WebArchive Extractor | Open Source |
| .WEBM | Google | Arquivos de vídeo | WebM Video File | Eltima Elmedia Player | Open Source |
| .WEBP | Google | Arquivos de imagem Raster | Google Image File Format | IrfanView | Open Source |
| .WGM | Open Source | Arquivos de jogos | Chalk Game Data | Chalk | Open Source |
| .WGT | Interscape | Arquivos de dados | IMPS Data File | Xwindow Neuro Bio Clusters | Open Source |
| .WHTT | Open Source | Arquivos Web | HTTrack Website Copier File | HTTrack | Open Source |
| .WI | Open Source | Arquivos de imagem Raster | Wavelet Image | DjVu Reader | Open Source |
| .WIM | Microsoft Corporation | Arquivos de imagem de disco | Windows Imaging Format File | ExtractNow | Open Source |
| .WINGS | Open Source | Arquivos 3D | Wings 3D File | Wings 3D | Open Source |
| .WK! | IBM | Arquivos de planilha | Lotus 1-2-3 Spreadsheet | Gnumeric | Open Source |
| .WK1 | IBM | Arquivos de dados | Lotus Worksheet | Gnumeric | Open Source |
| .WK4 | IBM | Arquivos de dados | Lotus Lotus 1-2-3 V4 Worksheet | Gnumeric | Open Source |
| .WKB | Corel | Arquivos de Texto | Corel WordPerfect Document | PostGIS | Open Source |
| .WMA | Microsoft Corporation | Arquivos de áudio | Windows Media Audio File | Eltima Elmedia Player | Open Source |
| .WML | Syncro Soft | Arquivos Web | Wireless Markup Language File | AbiWord | Open Source |
| .WMV | Microsoft Corporation | Arquivos de vídeo | Windows Media Video File | Eltima Elmedia Player | Open Source |
| .WN | WN | Arquivos Web | WN Web File | WN | Open Source |
| .WOFF | Open Source | Arquivos de fonte | Web Open Font Format File | FontForge | Open Source |
| .WOW | Open Source | Arquivos de áudio | Grave Composer Music Module | OpenMPT | Open Source |
| .WOWPROJ | Open Source | Arquivos de desenvolvedor | AddOn Studio Project File | Addon Studio for World of Warcraft | Open Source |
| .WPB | PGN Inc. | Arquivos de imagem Raster | OpenCanvas 1.1 Image | Windows Phone Device Manager | Open Source |
| .WPJ | Watcom International Corporation | Arquivos miscelâneas | Watcom C/C++ Project | Watcom C/C++ | Open Source |
| .WPT | Corel | Arquivos de Texto | WordPerfect Template | Cube 2 Sauerbraten | Open Source |
| .WR! | IBM | Arquivos de planilha | Lotus 1-2-3 Spreadsheet | Gnumeric | Open Source |
| .WRD | Open Source | Arquivos de Texto | COREX Manually Verified Word Segmentation Data | COREX | Open Source |
| .WRL | Unknown Developer | Arquivos 3D | VRML World | FreeWRL | Open Source |
| .WRZ | Parallel Graphics | Arquivos 3D | Compressed VRML World File | FreeWRL | Open Source |
| .WS | MicroPro International Corp. | Arquivos de Texto | WordStar Document | OpenEmu | Open Source |
| .WSC | Open Source | Arquivos de jogos | WonderSwan Color Game ROM | Oswan | Open Source |
| .WSIM | Open Source | Arquivos Web | FirstStop WebSearch Import Module | FirstStop WebSearch | Open Source |
| .WSR | Genius Media Group | Arquivos de dados | Crossword Genius Data | FirstStop WebSearch | Open Source |
| .WUL | Open Source | Arquivos miscelâneas | WinUHA Language File | WinUHA | Open Source |
| .WV | David Bryant | Arquivos de áudio | WavPack Audio File | XMMS | Open Source |
| .WVC | Open Source | Arquivos de áudio | WavPack Correction File | WavPack | Open Source |
| .WVE | Wondershare Software Co., Ltd. | Arquivos de vídeo | Wondershare Filmora Project File | SoX | Open Source |
| .WVL | Open Source | Arquivos de imagem Raster | Wavelet Image | DjVu Reader | Open Source |
| .WVM | Google | Arquivos de vídeo | Google Play Video File | HandBrake | Open Source |
| .WX | Open Source | Arquivos de cópia | Wanam Xposed Backup File | Wanam Xposed | Open Source |
| .WXM | Open Source | Arquivos miscelâneas | wxMaxima Batch File | wxMaxima | Open Source |
| .WXP | Open Source | Arquivos de vídeo | Wax 2.0 Project | DebugMode Wax | Open Source |
| .WXR | Open Source | Arquivos de dados | WxWindgets Resource Data | wxWidgets | Open Source |
| .WZ | Nexon | Arquivos de jogos | MapleStory Game Data File | Warzone 2100 | Open Source |
| .X13 | DarXabre | Arquivos de jogos | Hooligans Game Archive File | Dragon UnPACKer | Open Source |
| .X64 | Commodore International | Arquivos de imagem de disco | Commodore 64 Disk Image | VICE | Open Source |
| .XA | Electronic Arts | Arquivos de áudio | The Sims Audio File | PSMplay | Open Source |
| .XA2 | Csabo | Arquivos de jogos | XWE Data File | XWE | Open Source |
| .XAC | Tilted Mill Entertainment | Arquivos de jogos | SimCity Societies Game File | GnuCash | Open Source |
| .XAF | Autodesk, Inc. | Arquivos 3D | 3ds Max XML Animation File | Cal3DViewer | Open Source |
| .XAR | Magix Software GmbH | Arquivos de imagem vector | Xara Xtreme Drawing | Xara Xtreme for Linux | Open Source |
| .XBEL | Python Software Foundation | Arquivos Web | XBEL Bookmarks File | Arora | Open Source |
| .XBL | Open Source | Arquivos de desenvolvedor | XBLite Source Code File | XBLite | Open Source |
| .XBM | Unknown Developer | Arquivos de imagem Raster | X11 Bitmap Graphic | IrfanView | Open Source |
| .XCF | Gimpel Software | Arquivos de imagem Raster | GIMP Image File | IrfanView | Open Source |
| .XDC | Adobe Systems Incorporated | Arquivos de configuração | Adobe Acrobat Printer Description | DarkCrypt IV | Open Source |
| .XDELTA | Open Source | Arquivos comprimidos | Xdelta Binary Differential File | xdelta | Open Source |
| .XDF | NASA | Arquivos de imagem de disco | Extended Disk Format Image | TunerPro | Open Source |
| .XEN | Activision | Arquivos de jogos | Guitar Hero 3 Data File | Xenu's Link Sleuth | Open Source |
| .XGP | Open Source | Arquivos de dados | Xfire Game Patcher File | XGP | Open Source |
| .XHD | Open Source | Arquivos miscelâneas | HappyFish XML Data File | HappyFish | Open Source |
| .XI | Starbreeze Studios | Arquivos de áudio | Fasttracker 2 Extended Instrument File | MilkyTracker | Open Source |
| .XKM | Open Source | Arquivos de dados | X KeyBoard File | Linux | Open Source |
| .XL | Microsoft Corporation | Arquivos de planilha | Excel Spreadsheet | XBLite | Open Source |
| .XLF | Open Source | Arquivos de dados | XLIFF Document | OmegaT | Open Source |
| .XLS | Microsoft Corporation | Arquivos de planilha | Microsoft Excel 97 To 2003 Spreadsheet | Gnumeric | Open Source |
| .XM | Starbreeze Studios | Arquivos de áudio | FastTracker 2 Extended Module | ModPlug Player | Open Source |
| .XMCD | Parametric Technology Corporation | Arquivos de dados | Mathcad Worksheet File | SMath Studio | Open Source |
| .XMF | Open Source | Arquivos 3D | Cal3D XML Mesh File | Cal3DViewer | Open Source |
| .XML | Wattle Software | Arquivos de dados | XML File | AbiWord | Open Source |
| .XMZ | Starbreeze Studios | Arquivos de áudio | FastTracker 2 Extended Module | ModPlug Player | Open Source |
| .XP3 | Open Source | Arquivos de jogos | KiriKiri Package File | XP3 / Kirikiri tools | Open Source |
| .XPF | Open Source | Arquivos de áudio | Linux MultiMedia Studio Preset File | LMMS | Open Source |
| .XPM | XnSoft | Arquivos de imagem Raster | X11 Pixmap Graphic | IrfanView | Open Source |
| .XPY | Open Source | Arquivos de configuração | XPY Settings File | XPY | Open Source |
| .XQL | Open Source | Arquivos de desenvolvedor | XML Query Language File | MacVim | Open Source |
| .XR | Red Hat | Arquivos de desenvolvedor | Cygwin Ld-scripts Data | Cygwin | Open Source |
| .XR2 | Open Source | Arquivos de dados | Xrecode II Registration | Xrecode | Open Source |
| .XRF | Open Source | Arquivos 3D | Cal3D XML Materials File | Cal3DViewer | Open Source |
| .XRL | SAP | Arquivos de dados | PowerDesigner Report File | XML Résumé Library | Open Source |
| .XS3 | Open Source | Arquivos de planilha | XESS Worksheet | Xess | Open Source |
| .XS4 | Open Source | Arquivos de planilha | XESS Worksheet | Xess | Open Source |
| .XS5 | Open Source | Arquivos de planilha | XESS Worksheet | Xess | Open Source |
| .XSF | Microsoft Corporation | Arquivos de dados | InfoPath Form Definition File | Cal3DViewer | Open Source |
| .XSP | Open Source | Arquivos de áudio | Kodi Smart Playlist File | Kodi | Open Source |
| .XSPF | VideoLAN | Arquivos de áudio | XSPF Playlist File | Clementine | Open Source |
| .XVG | Open Source | Arquivos de Texto | Grace Document | GRACE | Open Source |
| .XVID | DivX, LLC. | Arquivos de vídeo | Xvid-Encoded Video File | Eltima Elmedia Player | Open Source |
| .XVO | Open Source | Arquivos de dados | RatDVD Internal File | RatDVD | Open Source |
| .XYZ | SourceForge | Arquivos de dados | Molecule Specification File | Avogadro | Open Source |
| .XZ | Various Developers | Arquivos comprimidos | XZ Compressed Archive | ExtractNow | Open Source |
| .Y | Microsoft Corporation | Arquivos de imagem Raster | Subsampled Raw YUV Image | AbiWord | Open Source |
| .YAB | Open Source | Arquivos de desenvolvedor | Yabasic Source Code | Yabasic | Open Source |
| .YDK | Open Source | Arquivos de jogos | Yu-Gi-Oh! Deck File | YGOPRO | Open Source |
| .YENC | Open Source | Arquivos codificados | yEnc File | yDec | Open Source |
| .YGD | Open Source | Arquivos de áudio | YouGooDai Playlist File | YouGooDai | Open Source |
| .YM | Atari Corporation | Arquivos de áudio | Atari ST Audio File | ST-Sound | Open Source |
| .YMP | Open Source | Arquivos de desenvolvedor | YaST Metapackage File | YaST | Open Source |
| .YNC | Open Source | Arquivos codificados | yEnc Encoded File | yDec | Open Source |
| .YSP | Open Source | Arquivos de imagem Raster | BYOB Sprite File | Snap! | Open Source |
| .YUV | WinXMedia Software | Arquivos de vídeo | YUV Video File | IrfanView | Open Source |
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