| .STV | Unknown Developer | Ficheiros de Dados | SofTV Authoring Data | Unknown Software | Unknown Developer |
| .SU | Unknown Developer | Uncommon Files | Country Code Top-level Domain | Unknown Software | Unknown Developer |
| .SVTREPORTER | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .SWD_RAP | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .SWR | Unknown Developer | Ficheiros de Dados | SageWorld Anti-Hacker Program File | Unknown Software | Unknown Developer |
| .SY# | Unknown Developer | Ficheiros de Cópia de Segurança | Darn! Backup File | Unknown Software | Unknown Developer |
| .SYMBOLS | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYMLINK | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SYNTAX | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYSLOG | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .S_S | Unknown Developer | Uncommon Files | Eru/erd File | Unknown Software | Unknown Developer |
| .TABLE1 | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TABLES | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TAL | Adobe Systems Incorporated | Ficheiros de Texto | Adobe TypeAlign Text Illustration File | Unknown Software | Unknown Developer |
| .TALK | Unknown Developer | Ficheiros de Dados | Text To Speech File | Unknown Software | Unknown Developer |
| .TALK2 | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TCO | Unknown Developer | Ficheiros de Dados | T9000 Object Module | Unknown Software | Unknown Developer |
| .TDT | Sony | Ficheiros de Vídeo | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TEASERS2 | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEBK | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TECH | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TELL | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEST | Unknown Developer | Ficheiros de Dados | Testing File | Unknown Software | Unknown Developer |
| .TESTING | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TFB | Unknown Developer | Uncommon Files | Unknown Apple II Data File | Unknown Software | Unknown Developer |
| .TFR | LucasArts Entertainment Company, LLC | Ficheiros de Jogo | TIE Fighter Pilot File | Unknown Software | Unknown Developer |
| .TG1 | Unknown Developer | Uncommon Files | On Target Project File | Unknown Software | Unknown Developer |
| .TGR | The U.S. Census Bureau | Ficheiros GIS | Tiger Line Data | Unknown Software | Unknown Developer |
| .THW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TICKET | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TID | Sony | Ficheiros de Vídeo | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TIK | Unknown Developer | Ficheiros de Desenvolvedor | Script File For Game Textures | Unknown Software | Unknown Developer |
| .TILE | XnSoft | Ficheiros de Imagem Raster | Eclipse Image | Unknown Software | Unknown Developer |
| .TIPS | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TJL | Unknown Developer | Ficheiros de Cópia de Segurança | VAXTPU Editor Backup File | Unknown Software | Unknown Developer |
| .TJT | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TJZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TKI | Unknown Developer | Uncommon Files | Mime: Application/x-tkined | Unknown Software | Unknown Developer |
| .TNL | Unknown Developer | Ficheiros de Imagem 3D | Thumbnail Image Format | Unknown Software | Unknown Developer |
| .TO | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRACKS | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRANSFERIR | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TRAVEL | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRIAL | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRIF | Tiling Task Group (TTG) | Ficheiros de Imagem Raster | Tiled Raster Interchange Format | Unknown Software | Unknown Developer |
| .TRUETYPE | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TSH | CENiX, Inc. | Ficheiros de Áudio | Cenix Audio | Unknown Software | Unknown Developer |
| .TTO | Unknown Developer | Uncommon Files | Client Access Data Specification File | Unknown Software | Unknown Developer |
| .TVLINK | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TVW | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TVX | Doug Cutting | Uncommon Files | Apache Lucene Term Vector Index File | Unknown Software | Unknown Developer |
| .TVZ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TWN | Unknown Developer | Ficheiros de Configurações | Scanner Settings File | Unknown Software | Unknown Developer |
| .TWO | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TXG | ESRI | Uncommon Files | Georeference Subobject File | Unknown Software | Unknown Developer |
| .TXM | CFP Software Limited | Ficheiros de Dados | CFPwinMan Document File | Unknown Software | Unknown Developer |
| .TYP | Unknown Developer | Uncommon Files | Thumbs32 File | Unknown Software | Unknown Developer |
| .TZG | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .U2C | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .U2E | Unreal Software | Uncommon Files | Unreal Game Translation | Unknown Software | Unknown Developer |
| .U4A | Unknown Developer | Ficheiros Executáveis | UnInstaller Archive File | Unknown Software | Unknown Developer |
| .U8 | Nintendo | Ficheiros de Jogo | Mario Kart Wii Archive File | Unknown Software | Unknown Developer |
| .UAD | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .UAP | Siemens AG | Ficheiros Compactados | SIMATIC WinCC User Archive Export | Unknown Software | Unknown Developer |
| .UB1 | Unknown Developer | Ficheiros de Vídeo | X-Driven DRS-1100 Recorded Video | Unknown Software | Unknown Developer |
| .UBF | Marker Communication | Ficheiros de Dados | MXT3010 Universal Boot Format | Unknown Software | Unknown Developer |
| .UBI | Ubisoft | Ficheiros de Jogo | Ubisoft Logo Animation | Unknown Software | Unknown Developer |
| .UCA | Unknown Developer | Uncommon Files | Unicode Collation Algorithm Data File | Unknown Software | Unknown Developer |
| .UCI | SysDevSoftware | Ficheiros de Cópia de Segurança | UFS Explorer Backup File | Unknown Software | Unknown Developer |
| .UK_ | Unknown Developer | Uncommon Files | Mcguiness File | Unknown Software | Unknown Developer |
| .UND | DHI | Ficheiros de Dados | MOUSE Urban Network Datafile | Unknown Software | Unknown Developer |
| .UNIX BAR COMPRESSED FILE ARCHIVE | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .UNKNOWN | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .UNM | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .UP | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .UPD | Various Developers | Ficheiros de Texto | Program Update Information | Unknown Software | Unknown Developer |
| .UPDATED | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .UVC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .UVZ | Unknown Developer | Ficheiros Compactados | DECE ZIP Compressed Data | Unknown Software | Unknown Developer |
| .UXR | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .V2Q | Texas Instruments, Inc. | Ficheiros de Dados | TI Voyage 200 Certificate File | Unknown Software | Unknown Developer |
| .V48 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .V50 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VAD | Blue Marble Geographics | Ficheiros de Dados | Mapper Variant | Unknown Software | Unknown Developer |
| .VAX | Unknown Developer | Uncommon Files | Pbm Plus File | Unknown Software | Unknown Developer |
| .VCMP | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VCY | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VC_ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VDH | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VDMPVF | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VDO | Unknown Developer | Ficheiros Executáveis | Heathen Virus File | Unknown Software | Unknown Developer |
| .VFF | Sun Microsystems | Ficheiros de Imagem Raster | Sun TAAC Graphic File | Unknown Software | Unknown Developer |
| .VHA | Macromedia | Uncommon Files | Macromedia Sitespring File | Unknown Software | Unknown Developer |
| .VHDPMEM | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VHP | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VIEWER | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .VLQ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .VMCZ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .VOICE | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .VOT | Unknown Developer | Ficheiros Raw de Câmera | Recorded Video File | Unknown Software | Unknown Developer |
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