| xmpskin | XMPlay Skin Data |
| xmptf | TextMap Portable Transcript Data |
| xmp_bin | Parasolid CAD Binary Partition Data |
| xmp_txt | Parasolid CAD ASCII Partition Data |
| xmr | M.O.L.E. MAP Machine Data |
| xmtb | FileMaker Pro Table Definitions Data |
| xmt_bin | Parasolid CAD Binary Parts Data |
| xmt_neu | Parasolid CAD ASCII Drawing Data |
| xmt_txt | Parasolid CAD ASCII Parts Data |
| xmu | eXtendable Wad Editor Data |
| xmx | Autodesk AutoCAD External Message File |
| xmzx | ExamSoft SofTest Exam Data |
| xnf | Extensible Numerical File Format Data |
| xng | FishXing Data |
| xnode | LabVIEW XNode Data |
| xnt | QuarkXPress Extension |
| xnv | nVision Layout |
| xo | Sugar Linux Application Bundle |
| xodo | Xodo Internal Data |
| xoj | Xournal Journal Data |
| xop | IGOR Pro Extension |
| xop | XML-Binary Optimized Packaging Data |
| xor | Xortool Results Data |
| xot | XGW Job Output Data |
| xpcm | X-Setup Pro Code Module |
| xpd | PlayStation Network Downloader Data |
| xpf | DB/TextWorks Exported Form Definitions |
| xpf | IMVU Morph Data |
| xpg | Autoplay Media Studio Exported Page |
| xpgt | Adobe InDesign XML Page Template File |
| xpk | DB/TextWorks Exported Record Skeleton Definitions |
| xpk | NMRView Peak List |
| xpl | LcdStudio Playlist |
| xpo | Microsoft Dynamics AX Export |
| xport | SAS XPORT Engine Data |