| tmx | Tiled Tile Map XML |
| tmy | Typical Meteorological Year Data |
| tmz | Medigraph Compressed Database |
| tmzip | Theme Manager Zip Package |
| tna | Topocad Net Adjustment |
| tnd | TranEd v2 File |
| tnd | CAS-Hydro Tree-node Definition File |
| tnef | Transport Neutral Encapsulation Format |
| tnf | Transport Neutral Encapsulation Format |
| tni | TexNet32 Database Index |
| tnj | CapturePost TimeStone Neo Job Data |
| tnk | Nimbus 7 SAMS Data File |
| tnt | TNT Data File |
| tnx | PageTech PCLTool Text Extraction File |
| tob | Zemax Object Data |
| toc | Eudora Addressbook TOC |
| tocf | Qualcomm Eudora for Mac TOC Data |
| tof | Mr. Photo Thumbnail |
| tog | TouchDesigner Geometry Data |
| tol | AOL Tool |
| ton | FMS32 Protocol Data |
| tool | Apple Terminal Data |
| top | GROMACS System Topology |
| top | E-Sword v8 Topic Note |
| topx | E-Sword v9 Topic Note |
| tot | LG Phone Rom |
| totalsbackup | Totals Database Backup File |
| totalsdb | Totals Database File |
| totalssyncdb | Kedisoft Totals Synchronized Database |
| tou | WRAP Tables Output Data |
