| 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 |
| yang | YANG Designer Document |
| yaodl | SGI PowerFlip YAODL 3D Image |
| yar | Yar Scene |
| ybk | Microsoft Encarta Yearbook |
| ydb | Yutori 7 Document |
| ydd | YANG Designer Document |
| ydl | SGI PowerFlip YAODL 3D Image |
| yes | Quick Bible Document |
| ygf | Y Graph Format |
| yka | Yenka Model |
| ymap | MindGenius v1 Document |
| z3d | ZModeler 3D Model |