| .T3D | Epic Games | Indstillingsfiler | Unreal Engine 3D Object File | Unreal Tournament | Epic Games |
| .T3M | Electric Rain | Indstillingsfiler | Swift 3D Material File | Swift 3D | Electric Rain |
| .TAM | TameDOS | Indstillingsfiler | Tame Program Settings | Tame | TameDOS |
| .TB | Tabbery | Indstillingsfiler | Tabbery Tab File | Tabbery | Tabbery |
| .TBB | Microsoft Corporation | Indstillingsfiler | Microsoft Office Toolbar Button | Microsoft Office | Microsoft Corporation |
| .TBE | Pegasys | Indstillingsfiler | TMPGEnc List | TMPGEnc | Pegasys |
| .TBM | Nabi Studios | Indstillingsfiler | Toribash Mod File | Toribash | Nabi Studios |
| .TBR | Adobe Systems Incorporated | Indstillingsfiler | Adobe Photoshop Custom Toolbar Preset | Adobe Photoshop | Adobe Systems Incorporated |
| .TDF | DVD Copy | Indstillingsfiler | Title Definition Format File | DVD X Copy | DVD Copy |
| .TEE | Steema Software | Indstillingsfiler | TeeChart Template | Steema TeeChart | Steema Software |
| .TESTRUNCONFIG | Microsoft Corporation | Indstillingsfiler | Microsoft Visual Studio Test Run Configuration File | Microsoft Visual Studio | Microsoft Corporation |
| .TF | Borland | Indstillingsfiler | Turbo Profiler Configuration | Turbo Profiler | Borland |
| .TFA | Tree Software and Consulting Inc. | Indstillingsfiler | TreeSoft CashFlow Analysis Data File | treeSoft CashFlow Analysis (tree.fa.exe) | treeSoft |
| .TFD | Various Developers | Indstillingsfiler | Tape Format Requirements Document | BAE Systems VITec PC | BAE Systems |
| .TFX | Avid Technology | Indstillingsfiler | Pro Tools Eleven Rack Plugin Preset File | Avid Pro Tools | Avid Technology |
| .TGB | TheGreenBow | Indstillingsfiler | IPSec VPN Client VPN Configuration File | IPSec VPN Client | TheGreenBow |
| .THE | Microsoft Corporation | Indstillingsfiler | Microsoft Plus! Theme File | Microsoft Plus! | Microsoft Corporation |
| .THEME | Microsoft Corporation | Indstillingsfiler | Microsoft Plus! Desktop Theme | Microsoft Windows | Microsoft Corporation |
| .THEMEPACK | Microsoft Corporation | Indstillingsfiler | Microsoft Windows 7 Theme Pack | Microsoft Windows 7 | Microsoft Corporation |
| .THM | Sony | Indstillingsfiler | Sony Ericsson Mobile Phone Theme File | Sony Ericsson Theme Creator | Sony Mobile Communications |
| .THMX | Microsoft Corporation | Indstillingsfiler | Microsoft Office 2007 Theme File | Microsoft Excel | Microsoft Corporation |
| .TIM | Sierra Entertainment | Indstillingsfiler | The Incredible Machine Level | The Incredible Machine | Sierra Entertainment |
| .TLL | LG Electronics | Indstillingsfiler | LG TV Link-Loader File | ChanSort | Open Source |
| .TLO | IBM | Indstillingsfiler | SPSS TableLooks File | IBM SPSS | IBM |
| .TMS | Telemate | Indstillingsfiler | Telemate Script | Telemate | Telemate |
| .TOP | KTH Royal Institute of Technology | Indstillingsfiler | Gromacs Topology File | Gromacs | KTH Royal Institute of Technology |
| .TP | SnapStream Media | Indstillingsfiler | Beyond TV Transport Stream File | CyberLink PowerDVD | CyberLink |
| .TPF | IBM | Indstillingsfiler | SPSS Text Wizard Document | IBM SPSS | IBM |
| .TPL | Unknown Developer | Indstillingsfiler | Document Template | NoteTab | Fookes Software |
| .TPP | Ternion Corporation | Indstillingsfiler | FLAMES GUI Template File | FLAMES | Ternion Corporation |
| .TR | Yadabyte | Indstillingsfiler | TomeRaider 2 eBook File | TomeRaider | Yadabyte |
| .TRW | Borland | Indstillingsfiler | Borland Turbo Debugger For Windows Session-State Settings | Borland Turbo Debugger | Borland |
| .TRX | Microsoft Corporation | Indstillingsfiler | Visual Studio Test Results File | Microsoft Visual Studio | Microsoft Corporation |
| .TSI | Native Instruments | Indstillingsfiler | Traktor Settings File | Traktor | Native Instruments |
| .TSK | Microsoft Corporation | Indstillingsfiler | Pocket PC Skin | Microsoft ActiveSync | Microsoft Corporation |
| .TSM | Beckhoff | Indstillingsfiler | TwinCAT System Manager Configuration File | TwinCat System Manager | Beckhoff |
| .TSP | Inmatrix Media Solutions | Indstillingsfiler | Digital TV DVR Recording | Zoom Player | Inmatrix Media Solutions |
| .TST | Measurement Computing | Indstillingsfiler | TestPoint Test File | Measurement Computing TestPoint | Measurement Computing |
| .TSW | National Instruments | Indstillingsfiler | NI TestStand Workspace | NI TestStand | National Instruments |
| .TSZ | Cerulean Studios | Indstillingsfiler | Trillian Skin File | Cerulean Studios Trillian | Cerulean Studios |
| .TV | Corel | Indstillingsfiler | Corel Paradox Table View Settings | Corel Paradox | Corel |
| .TVC | IMSI/Design, LLC | Indstillingsfiler | Turbo View & Convert Batch Presets File | IMSI TurboCAD Deluxe | Redway3d and others |
| .TVP | NVIDIA | Indstillingsfiler | NVIDIA Graphic Card Update File | NVIDIA Graphics Driver | NVIDIA |
| .TWC | Tripwire, Inc. | Indstillingsfiler | Tripwire Configuration Data File | Tripwire Enterprise | Tripwire, Inc. |
| .TWN | Unknown Developer | Indstillingsfiler | Scanner Settings File | Unknown Software | Unknown Developer |
| .TWS | Helios Software Solutions | Indstillingsfiler | TextPad Workspace | TextPad | Helios Software Solutions |
| .TXM | CFP Software Limited | Indstillingsfiler | CFPwinMan Document File | CFPwinMan | CFP Software Limited |
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