| xtm | XtremSplit Data |
| xtp | XTree Data |
| xtp | XTrkCAD Layout |
| xtpl | XER Manager Template |
| xtr | XTrkCad Demo |
| xtreme | Winstep Xtreme Theme Pack |
| xtrl | XTND Translator Data |
| xts | IMPS Data |
| xtt | X TimeTable Data |
| xtxt | Xtext Data |
| xui | Xbox 360 User Interface Data |
| xur | Xbox 360 User Interface Binary Data |
| xus | UpdateStar Data |
| xvg | Grace Document |
| xvo | RatDVD Internal Data |
| xvp | XView Package |
| xvs | XView Scene Package |
| xvu | Comodo BOClean Definitions |
| xvv | Placevent 3D-RISM Results Data |
| xvw | MAPublisher View Data |
| xwav | eXtendable Wad Editor XWAV Data |
| xwz | X-Setup Pro Wizard Data |
| xx | Xxencoded Data |
| xxe | Xxencoded Data |
| xxi | GameSpy Arcade Data |
| xxl | Xilog Plus XXL File |
| xxx | Singer XL Embroidery Data |
| xya | ANUGA XYA Data |
| xyb | QuickWave 3D Batch List |
| xye | TOPAS Data |
| xyh | TunnelCAD Coordinate Data |
| xys | XYplorer Script |
| xyz | Celestia Trajectory File |
| xyz | Tinker Cartesian Coordinates |
| xyzv | Celestia v1.6 Trajectory File |