| 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 |
| ton | FMS32 Protocol Data |
| top | E-Sword v8 Topic Note |
| top | GROMACS System Topology |
| topx | E-Sword v9 Topic Note |
| tot | LG Phone Rom |
| totalsbackup | Totals Database Backup File |
| totalsdb | Totals Database File |
| tou | WRAP Tables Output Data |
| tp2 | WeiDU Resource Pack |
| tp5 | MODTRAN Tape 5 Data |
| tp6 | MODTRAN Standard Output File |
| tp7 | MODTRAN Primary Spectral Output |
| tp8 | MODTRAN Spectral Output Data |
| tpa | GROMACS ASCII Input File |
| tpb | GROMACS Binary Input File |
| tpdb8 | ThumbsPlus v8 Thumbnail Database |
| tpdb8s | ThumbsPlus JET Database |
| tpe | Clarion Example Database File |
| tped | PLINK Transposed Text Genotype Table |
| tpf | Topocad Profile Form |
| tph | PTC Creo Tool Path Storage Data |
| tpl | Trial Sequential Analysis Template |