| trn | Microsoft SQL Server Transaction Log |
| trn | CFX Transient File |
| tro | IBM Voice Type Data |
| trp | Topocad Road Profile |
| trp | TripMaker Document |
| trp | TrimeTool TRP Output |
| trr | GROMACS Trajectory File |
| trs | Table Retrieval System Document |
| trs | TrIDNet Serialized Definitions Package |
| trt | Team Sports Scheduling System Report Template |
| truck | Rigs of Rods Truck Description File |
| trv | Topocad Traverse Document |
| trxml | Textkernel Sourcebox XML Data |
| try | CIBSE Test Reference Year Data |
| trz | Norton Antivirus Rapid Release Definition Update |
| ts2 | Time Stamp Project-wide Information |
| tsa | Trial Sequential Analysis Data |
| tsc | TINA v6 Schematic Data |
| tsg | TSG Data |
| tsj | Topcon TopSURV Job |
| tsk | Task Coach Data |
| tsm | TINA Subcircuit Macro |
| tso | The Studio Organizer Data |
| tst | Topocad Section Template |
| tstest | Telerik Test Studio Test Definitions File |
| tstream | SwarmPlayer Streaming Torrent |
| tsw | NI TestStand Workspace |
| tsx | Tiled Tile Set XML |
| tsz | Trillian Skin File |
| tt13 | Intuit TurboTax Canada 2013 Tax Return Data |
| tt14 | Intuit TurboTax Canada 2014 Tax Return Data |
| tt2 | Evergreen TPAC Template Page |
| ttd | Tinytag Data Logger Data |
| ttf | Altera Tabular Text File |
| tti | Teletext Page Document |
