| xtd | LabChip XT Data |
| xte | LabChip XTe Data |
| xterme | Winstep Xtreme Theme |
| xtf | LS-DYNA Extra Time History Database |
| xtic | ActivInspire Ticker Data |
| 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 | RealArcade Compressed Data |
| 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 |
| xtx | Xtext Data |
| xtxt | Xtext Data |
| xui | Xbox 360 User Interface Data |
| xule | XBRL Rules Data |
| xulrunner | XULRunner Data |
| xum | Excel CAPE-OPEN Unit Operation Model Data |
| xur | Xbox 360 User Interface Binary Data |
| xus | UpdateStar Data |
| xvas | eXtendable Wad Editor XVAS Data |
| xvg | Grace Document |
| xvo | RatDVD Internal Data |
