| xpr3 | QuarkXPress for Mac Document |
| xps | XML Paper Document |
| xpwe | PriMus XML Exchange Document |
| xs3 | XESS Worksheet |
| xs4 | XESS Worksheet |
| xs5 | XESS Worksheet |
| xscscpt | Transcribe! Script |
| xsd | Microsoft InfoPath XML Schema |
| xsf | Microsoft InfoPath Form Definition |
| xsh | Xshade 3D Model |
| xsl | Extensible Stylesheet Language Transformations |
| xslt | Extensible Stylesheet Language Transformations |
| xsn | Microsoft InfoPath Form Template |
| xssr | Microsoft SharePoint Workspace Data |
| xsx | Microsoft XML Schema Designer View |
| xtg | QuarkXPress Tags File |
| xtps | xTeam Document |
| xtrn | Call Report Pro XBRL Instance Document |
| xv0 | Extensible Virtual World Description Language Document |
| xv1 | Extensible Virtual World Description Language Document |
| xv2 | Extensible Virtual World Description Language Document |
| xv3 | Extensible Virtual World Description Language Document |
| xvi | XTherion Vector Image |
| xvl | Extensible Virtual World Description Language Document |
| xwf | OmniPage Workflow |
| xxn | Dimenzo Text Editor Document |
| xy | XyWrite Document |
| xy3 | XyWrite III Document |
| xy4 | XyWrite IV Document |
| xyd | XYPad Drawing Document |
| xyp | XyWrite III Plus Document |
| xyw | XyWrite IV Document |
| xzfx | ZipLogix ZipForm Transaction |
| xzip | Hungarian Tendering System Document |
| yak | KayakFoundry 3D Design Documen |