| xtk | X-Ray Toolkit Metadata |
| xtm | XtremSplit Data |
| xtmp | Avid Xpress Pro Template |
| xtp | XTree Data |
| xtp | XTrkCAD Layout |
| xtp2 | Microsoft InfoPath Form Template Part |
| xtpl | XER Manager Template |
| xtr | XTrkCad Demo |
| xtreme | Winstep Xtreme Theme Pack |
| xtrl | XTND Translator Data |
| xts | IMPS Data |
| xtt | X TimeTable Data |
| xtu | Intel Extreme Tuning Utility 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 |
| xwdf | VooPoo Firmware Update Data |
| xwz | X-Setup Pro Wizard Data |
| xx | Xxencoded Data |
| xxd | Brixx Planner Calendar Data |
| xxe | Xxencoded Data |
| xxi | GameSpy Arcade Data |
| xxl | Xilog Plus XXL File |
| xxr | Brixx Planner Report Data |
| xxs | StruMM3D Structure Data |
| xxx | Singer XL Embroidery Data |