| wwi | WinWein Interchange Format Data |
| wwk | WAsP v7 Workspace |
| wwls | Weather Watcher Live Skin |
| wwq | SWAT Watershed Water Quality Input |
| wwr | WAsP v8 Resource Grid |
| wwtfig | WorldWide Telescope Constellation Figures Data |
| wwtl | WorldWide Telescope Layer Data |
| wwu | Wwise Work Unit |
| wxp | wxWidgets Package Description Data |
| wxw | Winradio Extended Wave Data |
| wyc | wyUpdate Compressed Client Data |
| wys | wyBuild Server Data |
| wyu | wyBuild Update Data |
| wzd | Sharp Wizard Data |
| wztheme | WinZip Theme Data |
| x00 | Paradox Secondary Index |
| x01 | Paradox Secondary Index |
| x02 | Paradox Secondary Index |
| x03 | Paradox Secondary Index |
| x04 | Paradox Secondary Index |
| x05 | Paradox Secondary Index |
| x06 | Paradox Secondary Index |
| x07 | Paradox Secondary Index |
| x08 | Paradox Secondary Index |
| x09 | Paradox Secondary Index |
| x1 | X1 Saved Search |
| x1s | X1 Search Saved Search |
| x36 | Xplorer360 Data |
| x3p | XML 3D Surface Profile |
| x3s | X3S Data |
| x61 | Lenovo ThinkPad X61 Bios Update |
| x83 | GAEB DA XML Data File |
| xa | Chiron NRG Exported Dictionary |
| xac | GnuCash Data |
| xac | XMetaL Author Customization File |