| xcp | XLNT Script |
| xcplugin | Xcode Plug-in |
| xcscheme | Xcode Scheme Document |
| xcss | RichFaces XCSS File |
| xct | XVI32 Conversion File |
| xct | Xilinx PARTGen Partlist File |
| xdf | ProWorx NXT Extended Memory Data File |
| xdf | Extensible Data Format File |
| xdfz | Compressed Extensible Data Format File |
| xdt | Xscript Data File |
| xfdl | XPLATFORM Screen Form Definition |
| xfl | Adobe Flash Exchange File |
| xgr | GraphEdit Filter Graph Markup Language |
| xib | Apple Interface Builder Development-Time Resources |
| xil | Xilize Markup Source |
| xilinc | Xilize Include |
| xin | OmniMark Include File |
| xje | XJEase Source Code |
| xl | XBLite Source Code |
| xmla | XML for Analysis File |
| xnb | XNA Game Studio Binary Package |
| xob | WeintekHMI EasyBuilder 8000 XOB File |
| xpb | XPB! Basic Source Code |
| xpk | Xscript Package |
| xpp | X++ Source Code |
| xq | XQuery File |
| xql | XML Query Language |
| xqm | Oxygen XML Editor XQuery Module |
| xquery | XQuery File |
| xqy | XQuery File |
| xrc | wxWidgets XML Based Resource |
| xrd | XRK Data File |
| xrg | Xscript Registry Data |
| xsc | Dataset Designer Internal Data |
| xsc | Xscript Script |
