| .TAB | Microsoft Corporation | Tekstitiedostot | Tab Separated Data File | Microsoft Excel | Microsoft Corporation |
| .TAL | Adobe Systems Incorporated | Tekstitiedostot | Adobe TypeAlign Text Illustration File | Adobe TypeAlign | Adobe Systems Incorporated |
| .TBASIC | Eros Olmi | Tekstitiedostot | ThinBasic Script | thinBasic | Eros Olmi |
| .TCM | IMSI/Design, LLC | Tekstitiedostot | TurboCAD Mac Drawing | IMSI TurboCAD Deluxe | Redway3d and others |
| .TDF | DVD Copy | Tekstitiedostot | Title Definition Format File | DVD X Copy | DVD Copy |
| .TDO | Xilinx, Inc. | Tekstitiedostot | Xilinx Text Design Output Data | Xilinx CORE Generator System | Xilinx, Inc. |
| .TEM | E J Software | Tekstitiedostot | Badge Designer 2000 Data | Badge Designer 2000 | E J Software |
| .TEMPLATE | Apple | Tekstitiedostot | Apple Pages Template | Apple Pages | Apple |
| .TEX | Open Source | Tekstitiedostot | LaTeX Source Document | gVim | Open Source |
| .TEXT | Sublime HQ Pty Ltd | Tekstitiedostot | Plain Text File | Microsoft Notepad | Microsoft Corporation |
| .TEXTCLIPPING | Apple | Tekstitiedostot | Mac OS X Text Clipping File | Apple Finder | Apple |
| .TGP | Planetside Software | Tekstitiedostot | Terragen Plugin | Planetside Software Terragen | Planetside Software |
| .THP | thakis | Tekstitiedostot | Wii/GameCube Video File | thpplay | thakis |
| .THR | PTC | Tekstitiedostot | Pro/ENGINEER File | Pro/ENGINEER | PTC |
| .TLB | Various Developers | Tekstitiedostot | VAX Text Library | Apple TextEdit | Apple |
| .TLD | The Eclipse Foundation | Tekstitiedostot | Tag Library Descriptor File | Notepad++ | Don Ho |
| .TLSET | BINProjects | Tekstitiedostot | Customization (Settings) File | Text Locker | BINProjects |
| .TLW | TLWallaceNET Publishing Inc. | Tekstitiedostot | TLWallace.NET Document | TLWallace.NET | TLWallaceNET Publishing Inc. |
| .TMD | SoftMaker Software | Tekstitiedostot | TextMaker Document | Softmaker Office | SoftMaker Software |
| .TMV | SoftMaker Software | Tekstitiedostot | TextMaker Template | Softmaker Office | SoftMaker Software |
| .TODO | Open Source | Tekstitiedostot | Simple Project ToDo Database | Simple Project ToDo | Open Source |
| .TPH | Borland | Tekstitiedostot | Turbo Pascal Help File | Turbo Pascal | Embarcadero Technologies |
| .TPL | Unknown Developer | Tekstitiedostot | Document Template | NoteTab | Fookes Software |
| .TTE | Microsoft Corporation | Tekstitiedostot | Private Character Editor File | Microsoft Private Character Editor | Microsoft Corporation |
| .TTF | Apple | Tekstitiedostot | TrueType Font | CorelDRAW Graphics Suite | Corel |
| .TTW | IBM | Tekstitiedostot | IBM Rational Tau Workspace | Rational Tau | IBM |
| .TUN | High Voltage Software | Tekstitiedostot | LEGO Racers Audio File | Audacity | Open Source |
| .TWD | SimTech | Tekstitiedostot | MindMapper Brainstorm And Visual Map | MindMapper | SimTech |
| .TX8 | Microsoft Corporation | Tekstitiedostot | DOS Text File | Notepad++ | Don Ho |
| .TXA | Sentel Advance | Tekstitiedostot | Midas ViewPoint Text Array List | Sentel Advance Midas ViewPoint | Sentel Advance |
| .TXD | DK22Pac | Tekstitiedostot | Game Texture Dictionary | Magic.TXD | DK22Pac |
| .TXE | Open Source | Tekstitiedostot | Enriched Text File | Microsoft Notepad | Microsoft Corporation |
| .TXK | Unknown Developer | Tekstitiedostot | Karaoke Song Lyrics | KaraDOS | Unknown Developer |
| .TXT | Sublime HQ Pty Ltd | Tekstitiedostot | Plain Text File | Microsoft Notepad | Microsoft Corporation |
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