| .T04 | Tobias Svensson | 3D Image Files | Top 4 Compressed Data File | top 4 | Unknown Developer |
| .TABLE1 | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TABLES | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TAL | Adobe Systems Incorporated | Text Files | Adobe TypeAlign Text Illustration File | Unknown Software | Unknown Developer |
| .TALK | Unknown Developer | Data Files | Text To Speech File | Unknown Software | Unknown Developer |
| .TALK2 | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TASP | Unknown Developer | Game Files | Strategy Planner Data File | Tactical Assault Strategy Planner | Unknown Developer |
| .TCO | Unknown Developer | Data Files | T9000 Object Module | Unknown Software | Unknown Developer |
| .TDR | PO KSI | Backup Files | ArVid Tape Backup | Top Draw | Unknown Developer |
| .TDT | Sony | Video Files | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TEASERS2 | Apple | Data Files | 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 | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEK | Unknown Developer | Data Files | ASITIC Technology File | ASITIC | Unknown Developer |
| .TELL | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEMP | Safer Networking Ltd. | Uncommon Files | Temporary (Temp) File | Original Program That Created The File | Unknown Developer |
| .TEST | Unknown Developer | Data Files | Testing File | Unknown Software | Unknown Developer |
| .TESTING | Apple | Data Files | 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 | Game Files | 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 | GIS Files | Tiger Line Data | Unknown Software | Unknown Developer |
| .THML | Unknown Developer | Developer Files | Theological HTML Document | Theological Markup Language (ThML) | Unknown Developer |
| .THW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .TICKET | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TID | Sony | Video Files | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TIK | Unknown Developer | Developer Files | Script File For Game Textures | Unknown Software | Unknown Developer |
| .TILE | XnSoft | Raster Image Files | Eclipse Image | Unknown Software | Unknown Developer |
| .TIPS | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TJL | Unknown Developer | Backup Files | 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 | 3D Image Files | Thumbnail Image Format | Unknown Software | Unknown Developer |
| .TO | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TOAD | Unknown Developer | Uncommon Files | FunkyToad System File | FunkyToad Network | Unknown Developer |
| .TRACKS | Apple | Data Files | 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 | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRD | Marco Pontello | Data Files | TrID Definitions Package | TR Assistant | Unknown Developer |
| .TRIAL | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRIF | Tiling Task Group (TTG) | Raster Image Files | Tiled Raster Interchange Format | Unknown Software | Unknown Developer |
| .TRUETYPE | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TSH | CENiX, Inc. | Audio Files | Cenix Audio | Unknown Software | Unknown Developer |
| .TTO | Unknown Developer | Uncommon Files | Client Access Data Specification File | Unknown Software | Unknown Developer |
| .TTS | SumTotal Systems | Data Files | ToolBook Translation System File | TrueTime | 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 | Settings Files | Scanner Settings File | Unknown Software | Unknown Developer |
| .TWO | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TXG | ESRI | Uncommon Files | Georeference Subobject File | Unknown Software | Unknown Developer |
| .TXK | Unknown Developer | Text Files | Karaoke Song Lyrics | KaraDOS | Unknown Developer |
| .TXM | CFP Software Limited | Data Files | CFPwinMan Document File | Unknown Software | Unknown Developer |
| .TXW | Yamaha Corporation | Audio Files | Yamaha TX16W Audio File | TX16WConverter | Unknown Developer |
| .TY2 | Unknown Developer | Uncommon Files | Gualtieri Theme Maker File | Gualtieri Theme Maker | 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 |
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