| tt | Visual Studio T4 Text Template |
| tte | TextTransformer Interpreter |
| tti | TextTransformer Script |
| ttr | TextTransformer Productions |
| ttt | TextTransformer Tests |
| ttw | IBM Rational Tau Workspace |
| ttx | TextTransformer Tokens |
| tu | Turing Unit File |
| tup | Tup Data |
| tur | Turing Source Code |
| tvsconfig | RAD Studio Modeling Configuration |
| twig | Twig Template |
| txg | Toad Data Modeler Package |
| txl | TXL Source Code |
| txs | Tiny XML Server Script |
| tzjs | Turbulenz Java Application |
| tzo | Turbulenz Object |
| u2 | IBM Rational Tau U2 Model |
| ubl | TI DaVinci User Boot Loader |
| udd | OllyDbg Module Info |
| udo | RapidPLUS User Defined Object |
| uf | Crestron SIMPL Compile |
| ui | QT User Interface File |
| uic | COCO Unit ICon File |
| uic | Aveva CAF User Interface Customization File |
| uir | NI LabWindows User Interface Resource File |
| ulb | COBOL Unisys Library File |
| ulc | RevaSoft ULC Application |
| ulp | EAGLE User Language Program |
| umc | Crestron SIMPL User Module |
| uml | Unified Modeling Language File |
| uml | StarUML v1 Model Data |
| upkg | Unreal Enigine Package Flags |
| urf | ProWorx NXT User Configurable Register Editor Data |
| urr | Uniface Runtime Repository |
