| .X-PNG | The Pixelmator Team | Arquivos de imagem Raster | Portable Network Graphics | Apple Safari | Apple |
| .XBL | Open Source | Arquivos de desenvolvedor | XBLite Source Code File | Apple Safari | Apple |
| .XCAPPDATA | Apple | Arquivos de desenvolvedor | Xcode App Data File | Apple Xcode | Apple |
| .XCARCHIVE | Apple | Arquivos de desenvolvedor | Xcode Archive | Apple Xcode | Apple |
| .XCCRASHPOINT | Apple | Arquivos de desenvolvedor | Xcode Crash Point File | Apple Xcode | Apple |
| .XCODE | Apple | Arquivos de desenvolvedor | Xcode Project | Apple Xcode | Apple |
| .XCODEPROJ | Apple | Arquivos de desenvolvedor | Xcode Project | Apple Xcode | Apple |
| .XCPLUGIN | Apple | Arquivos de complementos | Xcode Plugin | Apple Xcode | Apple |
| .XCSCHEME | Apple | Arquivos de desenvolvedor | Xcode Scheme File | Apple Xcode | Apple |
| .XCUSERSTATE | Apple | Arquivos Temporários | Xcode Data | Apple Xcode | Apple |
| .XCWORKSPACE | Apple | Arquivos de desenvolvedor | Xcode Workspace File | Apple Xcode | Apple |
| .XFB | Apple | Arquivos de sistema | Xserve RAID Firmware Binary File | Apple Xserve RAID Admin | Apple |
| .XHTM | Opera Software | Arquivos Web | Extensible Hypertext Markup Language Document | Apple Safari | Apple |
| .XHTML | Opera Software | Arquivos Web | Extensible Hypertext Markup Language Document | Apple Safari | Apple |
| .XIB | Apple | Arquivos de desenvolvedor | Interface Builder File | Apple Interface Builder | Apple |
| .XIP | Apple | Arquivos comprimidos | MacOS Signed Archive | Apple Archive Utility | Apple |
| .XLF | Open Source | Arquivos de dados | XLIFF Document | Apple TextEdit | Apple |
| .XLS | Microsoft Corporation | Arquivos de planilha | Microsoft Excel 97 To 2003 Spreadsheet | iWork | Apple |
| .XLSX | Microsoft Corporation | Arquivos de planilha | Microsoft Excel Open XML Spreadsheet | iWork | Apple |
| .XMAS | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .XSEND | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .XVID | DivX, LLC. | Arquivos de vídeo | Xvid-Encoded Video File | Apple QuickTime Player | Apple |
| .XXXX | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .Y | Microsoft Corporation | Arquivos de imagem Raster | Subsampled Raw YUV Image | Apple QuickTime Player | Apple |
| .ZIP | Winrar | Arquivos comprimidos | Zipped File | Apple Archive Utility | Apple |
| .ZONE | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .ZPI | Winrar | Arquivos comprimidos | Zipped File | Apple Archive Utility | Apple |
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