| xseq | xLights Sequence Data |
| xsf | Xilinx CORE Generator Pin File |
| xsf | IMVU Skeleton Data |
| xsi | Softimage dotXSI 3D Model |
| xsiaddon | Softimage dotXSI Add-on |
| xsig | eCoFirma XAdES Signature Data |
| xsk | XKeyBrew Menu Data |
| xsm | Sybase PowerDesigner XML Model |
| xso | XKeyBrew Menu Data |
| xsp | MAPublisher XSP Data Source |
| xsprl | X-Setup Pro Data |
| xsprla | X-Setup Pro Data |
| xsr | Bentley GEOPAK XS List Report |
| xsr | Tekla Structures FabTrol Report |
| xssz | Oracle BI Publisher Style Template |
| xstb | TextBridge Pro Data |
| xstk | xStarter Task Data |
| xsu | UNICOM Sample User XML Data |
| xsvf | Xilinx Serial Vector Format |
| xsz | ZynAddSubFX Standalone Scale File |
| xtabs | CFi Explorer Tabset Data |
| xtb | LocoScript External Translation Table |
| 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 |