| wwt | WebDev Page Template |
| wxf | WinSQL Scheduled Task Script |
| wxi | WiX Include File |
| wxl | WiX Localization File |
| wxr | wxWidgets Resource Data |
| wxres | WinDev Automatic Test Results |
| wxs | WiX Source File |
| wxt | WinDev Automatic Test |
| x | Microsoft DirectX D3D Object |
| x | XBLite Source Code |
| 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 |
| xbw | SUP Hybrid Web Container Workflow |
| xcappdata | Xcode App Data |
| xcarchive | Xcode Archive |
| xcb | Visual C++ Command Bar Data |
| xcconfig | Xcode Configuration Settings |
| xcdatamodeld | Xcode Core Data Model |
| xcl | IAR System Linker Command File |
| xclangspec | Xcode Language Specification Data |
| xcmd | HyperCard External Commands |
| xcodeplugin | Xcode Plug-in |
| xcp | XLNT Script |
| xcplugin | Xcode Plug-in |
| xcscheme | Xcode Scheme Document |
| xcss | RichFaces XCSS File |
| xct | Xilinx PARTGen Partlist File |
| xct | XVI32 Conversion File |
| xdf | XCAP Diff Data |
| xdf | ProWorx NXT Extended Memory Data File |