| xpu | IBM SiteProtector X-press Update File |
| xpw | Accessible FormNet Data File |
| xpx | Accessible FormNet Data File |
| xqa | PX Windows Board Description Data |
| xqcn | QPST Content |
| xqp | I-Doser Temporary Data |
| xqt | SuperCalc Macro |
| xqx | XQX Printer Stream Data |
| xr | Chaos Desktop Reference File |
| xr2 | Xrecode II Registration Data |
| xr21 | Xrecode II Registration Data |
| xra | SPPAS Annotation Tool Data |
| xrb | GIS Web Template XML Resource Bundle |
| xrb | OpenOffice JAVA Language Translation XML |
| xrb | XMind Resource Bundle |
| xrdml | PANalytical XRD Instruments Data |
| xrds | eXtensible Resource Descriptor Sequence Data |
| xref | IBM AIX Cross Reference Data |
| xresult | Xcode Xresult Data |
| xrf | IMVU Material File |
| xrff | Weka eXtensible Attribute-Relation File Format Data |
| xri | XML for Requirements Interchange Data |
| xrio | OMICRON Test Universe Extended RIO Object |
| xrk | AiM Tech EVO4S Logger Data |
| xrl | OSCAR Rules Data |
| xrl | Rapidform XOR 3D Scan CAD Data |
| xrm-ms | Windows Vista Activation Certificate |
| xrnt | Renoise DSP Device-chains Data |
| xrr | Chiron NRG Runtime Report Data |
| xrt | Revolution Single-spectrum Xraytor Data |
| xry | XRY Data |
| xrz | AiM Tech EVO4S Logger Data |
| xs | Hummingbird Exceed Startup File |
| xsb | Sybase PowerDesigner XML Model Backup |
| xsb | XMLBeans XML Schema Binary |