| xwav | eXtendable Wad Editor XWAV Data |
| xwdf | VooPoo Firmware Update Data |
| xwz | X-Setup Pro Wizard Data |
| xx | Xxencoded Data |
| xxd | Brixx Planner Calendar Data |
| xxe | Xxencoded Data |
| xxi | GameSpy Arcade Data |
| xxl | Xilog Plus XXL File |
| xxr | Brixx Planner Report Data |
| xxs | StruMM3D Structure Data |
| xxx | Singer XL Embroidery Data |
| xy | ALEID2000 Coordinates Data |
| xya | ANUGA XYA Data |
| xyb | QuickWave 3D Batch List |
| xye | TOPAS Data |
| xyh | TunnelCAD Coordinate Data |
| xys | XYplorer Script |
| xyz | Celestia Trajectory File |
| xyz | Tinker Cartesian Coordinates |
| xyzc | Voxler 3D Geometry Data |
| xyznb | Exocad 3D Mesh Data |
| xyzv | Celestia v1.6 Trajectory File |
| xzp | Freestyle Dash Skin |
| x_b | Parasolid CAD Binary Parts Data |
| x_t | Parasolid CAD ASCII Parts Data |
| y01 | Corel Paradox Secondary Index |
| y02 | Corel Paradox Secondary Index |
| y03 | Corel Paradox Secondary Index |
| y04 | Corel Paradox Secondary Index |
| y05 | Corel Paradox Secondary Index |
| y06 | Corel Paradox Secondary Index |
| y07 | Corel Paradox Secondary Index |
| y08 | Corel Paradox Secondary Index |
| y09 | Corel Paradox Secondary Index |
| yah | HeartBeat Data |