| xadl | XPLATFORM Application Program Definition |
| xal | Open XAL Configuration |
| xamlx | Visual Studio Workflow Service |
| xap | XACT Project File |
| xat | XAT Template |
| xbl | XBLite Source Code |
| xbml | SAP Business One Studio Workflow Process Data |
| xcappdata | Xcode App Data |
| xcarchive | Xcode Archive |
| xcconfig | Xcode Configuration Settings |
| xcdatamodel | Xcode Core Data Model |
| xcdatamodeld | Xcode Core Data Model |
| xcl | IAR System Linker Command File |
| xcmd | HyperCard External Commands |
| xcodeplugin | Xcode Plug-in |
| xcp | XLNT Script |
| xcplugin | Xcode Plug-in |
| xcscheme | Xcode Scheme Document |
| xcsnapshots | Xcode Snapshot |
| xcss | RichFaces XCSS File |
| xct | Xilinx PARTGen Partlist File |
| xct | XVI32 Conversion File |
| xdf | ProWorx NXT Extended Memory Data File |
| xdf | Extensible Data Format File |
| xdfl | eXtensible Data Flow Language Document |
| xdfz | Compressed Extensible Data Format File |
| xdoclet | JBoss XDoclet Reference Data |
| xdt | Xscript Data File |
| xfdl | XPLATFORM Screen Form Definition |
| xfl | Adobe Flash Exchange File |
