| .XC2 | Haliplex Communications | Fichiers de paramètres | DACCS Configuration File | HPXView | Haliplex Communications |
| .XCI | Adobe Systems Incorporated | Fichiers de paramètres | Adobe Reader Font Mapping File | Adobe Reader | Adobe Systems Incorporated |
| .XCU | Apache Software Foundation | Fichiers de paramètres | OpenOffice.org Configuration File | Apache OpenOffice | Apache Software Foundation |
| .XDC | Adobe Systems Incorporated | Fichiers de paramètres | Adobe Acrobat Printer Description | Adobe Acrobat DC | Adobe Systems Incorporated |
| .XDR | Microsoft Corporation | Fichiers de paramètres | XML-Data Reduced File | Microsoft Notepad | Microsoft Corporation |
| .XEE | Microsoft Corporation | Fichiers de paramètres | Microsoft Expression Encoder Preset | Expression Encoder | Microsoft Corporation |
| .XEM | X-Genics Limited | Fichiers de paramètres | eManager Metered Units | X-Genics eManager | X-Genics Limited |
| .XEP | X-Genics Limited | Fichiers de paramètres | eManager File Packaging Information | X-Genics eManager | X-Genics Limited |
| .XES | X-Genics Limited | Fichiers de paramètres | eManager Skins Definition | X-Genics eManager | X-Genics Limited |
| .XET | X-Genics Limited | Fichiers de paramètres | eManager Process Definition | X-Genics eManager | X-Genics Limited |
| .XEV | X-Genics Limited | Fichiers de paramètres | eManager Auto-Update File | X-Genics eManager | X-Genics Limited |
| .XGS | Microsoft Corporation | Fichiers de paramètres | XACT Global Settings File | Microsoft XACT | Microsoft Corporation |
| .XIP | Apple | Fichiers de paramètres | MacOS Signed Archive | Apple Archive Utility | Apple |
| .XJS | Newforms Technologies | Fichiers de paramètres | Jindent Settings File | Jindent | Newforms Technologies |
| .XLB | Microsoft Corporation | Fichiers de paramètres | Excel Toolbars File | Microsoft Excel | Microsoft Corporation |
| .XM2 | LexisNexis | Fichiers de paramètres | TextMap Version 2 Case Format File | TextMap | LexisNexis |
| .XMS | Alexander Gross | Fichiers de paramètres | Music Studio Project | Alexander Gross Music Studio | Alexander Gross |
| .XPF | Open Source | Fichiers de paramètres | Linux MultiMedia Studio Preset File | LMMS | Open Source |
| .XPL | Interscape | Fichiers de paramètres | LcdStudio Playlist File | LCDStudio | Interscape |
| .XPX | Intercon Associates | Fichiers de paramètres | Intercon FormNet File | Accessible FormNet | Intercon Associates |
| .XPY | Open Source | Fichiers de paramètres | XPY Settings File | XPY | Open Source |
| .XRX | Microsoft Corporation | Fichiers de paramètres | Expression Encoder Media Profile Settings | Expression Encoder | Microsoft Corporation |
| .XS | Microsoft Corporation | Fichiers de paramètres | Age Of Empires 3 Map AI Generator | Microsoft Age of Empires | Ensemble Studios |
| .XST | IBM | Fichiers de paramètres | WebSphere Query Template | WebSphere Application Server | IBM |
| .XTODVD | VSO Software | Fichiers de paramètres | ConvertXtoDVD Project File | ConvertXtoDVD | VSO Software |
| .XTP | adnx | Fichiers de paramètres | xTime Project Document | xPlan | adnx |
| .XUI | Microsoft Corporation | Fichiers de paramètres | Xbox 360 User Interface File | Microsoft Visual Studio | Microsoft Corporation |
| .XVM | VMware | Fichiers de paramètres | VMware Console Configuration File | VMware Workstation | VMware |
| .XWK | Intel Corporation | Fichiers de paramètres | Crosstalk Communicator Keyboard Mapping | Intel Crosstalk Communicator | Intel Corporation |
| .XXS | Sorenson Media | Fichiers de paramètres | Sorenson Squeeze Settings File | Squeeze | Sorenson Media |
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