| xaa | XML Audit Data |
| xab | Microsoft Mail Addressbook Data |
| xac | GnuCash Data |
| xac | XMetaL Author Customization File |
| xadd | Microsoft Expression Web Add-in |
| xades | XAdES Signature |
| xadml | XML-Based Application Description Information |
| xaf | Autodesk 3D Studio MAX XML Animation |
| xaf | Cal3D XML Animation |
| xaf | IMVU Animation |
| xaiml | XAIML Chatterbot Database File |
| xao | SALOME Geometry XAO Data |
| xappl | Turbo Studio XML Application Configuration |
| xas | Pro/ENGINEER XAS File |
| xb0 | XTreeGold for Dos Help Data |
| xbb | DVIPDFMx Output File |
| xbckl | ApSIC Xbench Checklist Data |
| xbd | JAXB Schema Data |
| xbd | Xilinx Board Description Format Data |
| xbdr | Darkroom Booth Template |
| xbf | XAML Binary File |
| xbin | RegSupreme Pro Licence Data |
| xbn | Xnick Nick Backup Data |
| xbpkg | ApSIC Xbench Package |
| xbs | XnView Script |
| xc0 | XTreeGold for Dos Help Data |
| xc3 | Cast3D 3D Scene Data |
| xcbr | Sonic Workbench XPath Routing Rules |
| xcc | Fiery Color Profiler Locked Profile |
| xccdf | Extensible Configuration Checklist Description Format Data |
