| trm | Terminal Settings |
| tsi | NI Traktor Settings File |
| tsm | TwinCAT System Manager Configuration |
| ttb | BRLTTY Text Table Data |
| ttcfg | SIMATIC Trace Configuration Data |
| ttcfgx | SIMATIC Trace Configuration Data |
| tti | BRLTTY Text Subtable Data |
| tvc | TeamViewer Configuration |
| tvf | dBASE Table View Settings |
| tw3 | TCPWedge Configuration Data |
| twc | TTWin Configuration File |
| twn | OP9630 Scanner Settings |
| twn | TwinCalc Settings |
| twrps | TWRP Settings |
| txr | CorelDRAW Graphics Custom Settings Data |
| typeit4me | TypeIt4Me Clippings |
| tzi | Windows CE Time Zone Information |
| uae | WinUAE Configuration |
| uav | OpenPilot UAV Settings Data |
| ubb | BEA eLink Adapter Configuration |
| ubr | Web Capacity Analysis Tool Settings |
| uchr | Apple iOS Keyboard Layout |
| ucp | SmartWare Communications Profile |
| udc | Universal Data Connection |
| udcx | Universal Data Connection |
| uec | UltraEdit Saved Settings |
| ufi | UFOCapture V2 Settings |
| umb | MemMaker Configuration Backup File |
| umprofile | UltraMon Display Profile |
| unit | Systemd Unit Data |
| uns | Visual Navigation Suite Export Settings |
| upf | Bentley MicroStation User Preference File |
| upload | WebSTAR File Upload Option |
| upp | Unified Printer Parameter |
| upv | UniversalPlantViewer Configuration Data |