| tur | Turing Source Code |
| turboc3 | Borland Turbo C Makefile |
| tvsconfig | RAD Studio Modeling Configuration |
| twig | Twig Template |
| txg | Toad Data Modeler Package |
| txl | TXL Source Code |
| txs | Tiny XML Server Script |
| tyb | Ty-Basic Source Code |
| tzjs | Turbulenz Java Application |
| tzo | Turbulenz Object |
| u2 | IBM Rational Tau U2 Model |
| u2d | Intel Fortran Compiler Internal Build Data |
| ua | UaModeler Model Data |
| uber | Amazon Lumberyard Uber File |
| ubl | TI DaVinci User Boot Loader |
| uc3 | AVR32 UC3 Firmware Image |
| uca | Unicode Collation Algorithm Data |
| udd | OllyDbg Module Info |
| udn | Alpha Five User Definition Data |
| udo | RapidPLUS User Defined Object |
| udr | JADE Unstructured Data Resource |
| uem | UltraEdit Macro Source Code |
| uf | Crestron SIMPL Compile |
| uht | Amulet uHTML GUI Data |
| ui | QT User Interface File |
| uic | Aveva CAF User Interface Customization File |
| uic | COCO Unit ICon File |
| uih | Geoworks UI Compiler Espire Header |
| uir | NI LabWindows User Interface Resource File |
| uit | UIX XML Page Template |