| 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 |
| tt10 | TurboTax Canada 2010 Tax Return |
| tt11 | TurboTax Canada 2011 Tax Return |
| tt12 | TurboTax Canada 2012 Tax Return |
| tt13 | Intuit TurboTax Canada 2013 Tax Return Data |
| tt14 | Intuit TurboTax Canada 2014 Tax Return Data |
| tt2 | Evergreen TPAC Template Page |
| tt2012state | TurboTax 2012 State Tax Form |
| ttbk | Canadian TurboTax 2010 Backup |
| ttd | Tinytag Data Logger Data |
| ttf | Altera Tabular Text File |
| tti | Teletext Page Document |
| ttl | Tera Term Macro |
| ttn | Bentley InRoads Topologically Triangulated Network Data |
| tto | IBM AS/400 Transfer Request |
| ttsm | TTS Turbo Macros Data |
| ttv | TempTale Manager Desktop Data |
| ttx | WinTTX Teletext Data |
| ttx | Trados TagEditor File |
| tt_ | Compressed TTF File |
| tud | ThumbsPlus Graphics Database |
| tudb | AVG PC TuneUp Database |
