| Abbreviation | Definition |
|---|---|
| XSO | Ultrapico Expresso Project File |
| XSP | eXtensible Server Page document |
| XSS | Ability Office Spreadsheet |
| XST | Fulford Software Easy Cross Cross Stitch Design |
| XST | X-Tract XML Script |
| XSTEP | XStep DWI Maker File |
| XSU | Fortran Libf77 File |
| XSUM | Clapack File |
| XSW | Milnta APL Transfer Function |
| XT | Crosstalk Related File |
| XT | FastTracker Music track |
| XT* | Crosstalk Related File |
| XTB | LocoScript External Translation Table |
| XTD | XML Type Definition |
| XTG | QuarkXPress Tags File |
| XTM | CmapTools Exported Topic Map |
| XTP | XTree Data File |
| XTP | XTreeGold Overlay |
| XTR | RealArcade Compressed Data File |
| XTS | Babya Desktop Shell System Software Extension |