| .WINDOWSLIV | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .WINDOWSMED | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .WJE | Mariner Software | Ikke Almindelige Filer | WinJournal Entry | WinJournal | Mariner Software |
| .WKO | Applied Training Science | Ikke Almindelige Filer | Workout Template File | RippedPro | Applied Training Science |
| .WKSP | Tethys Solutions | Ikke Almindelige Filer | Workspace Macro Pro File | Workspace Macro Pro | Tethys Solutions |
| .WM5 | Unknown Developer | Ikke Almindelige Filer | Dyndlg2 File | Dyndlg2 | Unknown Developer |
| .WMH | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .WNK | Satish Kumar | Ikke Almindelige Filer | Wink Presentation | Wink | Satish Kumar |
| .WNS | Broderbund | Ikke Almindelige Filer | PrintShop Newsletter File | PrintShop | Broderbund |
| .WPJ | Watcom International Corporation | Ikke Almindelige Filer | Watcom C/C++ Project | Watcom C/C++ | Open Source |
| .WPU | Archaeopteryx Software, Inc. | Ikke Almindelige Filer | User-specific Project File | Wing IDE | Archaeopteryx Software, Inc. |
| .WRX | Progress Software Corporation | Ikke Almindelige Filer | Progress File | Progress | Progress Software Corporation |
| .WS1 | Microsoft Corporation | Ikke Almindelige Filer | WordStar For Windows 1 File | Microsoft Wordstar | Microsoft Corporation |
| .WSQ | UTAU Team | Ikke Almindelige Filer | UTAU File | UTAU | Vocal Synthesizer |
| .WSZ | Nullsoft | Ikke Almindelige Filer | Winamp Classic Skin | Nullsoft Winamp | Nullsoft |
| .WT | WildTangent | Ikke Almindelige Filer | Branded .X 3D Model File | WildTangent FATE | WildTangent |
| .WTC | Logitech | Ikke Almindelige Filer | Logitech Webcam File | Logitech Webcam Software | Logitech |
| .WTK | Interscape | Ikke Almindelige Filer | WinTalk URL Address | WinTalk | Interscape |
| .WTP | Satish Kumar | Ikke Almindelige Filer | Wink Template | Wink | Satish Kumar |
| .WUL | Open Source | Ikke Almindelige Filer | WinUHA Language File | WinUHA | Open Source |
| .WWD | Microsoft Corporation | Ikke Almindelige Filer | Works Wizard File | Microsoft Works | Microsoft Corporation |
| .WWK | Corel Corporation | Ikke Almindelige Filer | Corel WordPerfect Keyboard Layout File | Corel WordPerfect | Corel |
| .WWM | Dalin-Service | Ikke Almindelige Filer | WeeWheel File | WeeWheel | Dalin-Service |
| .WWZ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .WXB | Microsoft Corporation | Ikke Almindelige Filer | Windows Miscellaneous File | Microsoft Windows | Microsoft Corporation |
| .WXM | Open Source | Ikke Almindelige Filer | wxMaxima Batch File | wxMaxima | Open Source |
| .WXW | WiNRADiO | Ikke Almindelige Filer | WiNRADiO Extended Wave File | Unknown Software | Unknown Developer |
| .WYG | CAST Group of Companies Inc. | Ikke Almindelige Filer | WYSIWYG File | Cast Soft wysiwyg | CAST Software |
| .WYN | Freedom Scientific | Ikke Almindelige Filer | WYNN Document File | WYNN | Freedom Scientific |
| .X23 | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X2M | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X33 | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .X3M | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XACT | XactSystems | Ikke Almindelige Filer | XactScript File | Unknown Software | Unknown Developer |
| .XAK | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XB~ | Unknown Developer | Ikke Almindelige Filer | IC File | Unknown Software | Unknown Developer |
| .XGA | Piotr Fusik | Ikke Almindelige Filer | Atari Falcon Picture Image Format | Recoil | Piotr Fusik |
| .XGC | id Software | Ikke Almindelige Filer | GtkRadiant XML Game Config | GtkRadiant | id Software |
| .XHD | Open Source | Ikke Almindelige Filer | HappyFish XML Data File | HappyFish | Open Source |
| .XI1 | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .XLAT | DigiSoft Innovations | Ikke Almindelige Filer | An Unknown Apple II File | Golden Orchard | DigiSoft Innovations |
| .XLTD | Unknown Developer | Ikke Almindelige Filer | Thunder Temporary Data File | Unknown Software | Unknown Developer |
| .XLX | Interscape | Ikke Almindelige Filer | XoloX Incomplete Download File | XoloX | Interscape |
| .XMP | Adobe Systems Incorporated | Ikke Almindelige Filer | Extensible Metadata Platform File | Microsoft Notepad | Microsoft Corporation |
| .XNK | Microsoft Corporation | Ikke Almindelige Filer | Microsoft Exchange Public Folder Shortcut | Microsoft Exchange Server | Microsoft Corporation |
| .XNX | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .XPE | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XPN | Quest Software | Ikke Almindelige Filer | Quest Saved Explain Plan | Unknown Software | Unknown Developer |
| .XPR | Parametric Technology Corporation | Ikke Almindelige Filer | Pro/ENGINEER Part Instance Accelerator File | Dassault Systemes SolidWorks | Dassault Systèmes |
| .XT* | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .XUP | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XUW | Milinta | Ikke Almindelige Filer | Milnta APL Transfer Function | Milinta APL | Milinta |
| .XVID-TRL | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .XWF | Nuance | Ikke Almindelige Filer | OmniPage Workflow File | OmniPage | Nuance |
| .XWT | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XXX | BloodDolly | Ikke Almindelige Filer | TeslaCrypt 3.0 Ransomware Encrypted File | Tesla Decoder | BloodDolly |
| .XXZ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .Y2 | Michael J. Roberts | Ikke Almindelige Filer | TADS Interactive Fiction Development GUI File | TADS | Michael J. Roberts |
| .YAD | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YEAH | DigiSoft Innovations | Ikke Almindelige Filer | An Unknown Apple II File | Golden Orchard | DigiSoft Innovations |
| .YES | Yuku | Ikke Almindelige Filer | Quick Bible Document | Quick Bible | Yuku |
| .YIN | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YJF | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YKI | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YLM | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YNM | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YPK | MicroSim Corporation | Ikke Almindelige Filer | MicroSim PCBoard Mapping File | PCBoard | Clark Development Company, Inc. |
| .YRA | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YTS | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YUF | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .YV | DigiSoft Innovations | Ikke Almindelige Filer | An Unknown Apple II File | Golden Orchard | DigiSoft Innovations |
| .YZF | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .Z80 | Texas Instruments, Inc. | Ikke Almindelige Filer | TI-83 And 84 Plus Calculator File | TI-83 | Texas Instruments, Inc. |
| .ZAL | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZBI | Zebra Technologies | Ikke Almindelige Filer | Zebra ZBI-Developer Project | ZBI-Developer | Zebra Technologies |
| .ZBJ | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZBX | Unknown Developer | Ikke Almindelige Filer | Disk Volume Identification | Unknown Software | Unknown Developer |
| .ZCF | ZENRIN Co.,Ltd. | Ikke Almindelige Filer | ZCF.Document Files | Zcf Converter | ZENRIN Co.,Ltd. |
| .ZCH | Unknown Developer | Ikke Almindelige Filer | ZIG Game Construction Kit Data | Unknown Software | Unknown Developer |
| .ZCS | Synacor Inc. | Ikke Almindelige Filer | File Extension .zcs | Zimbra Collaboration | Synacor Inc. |
| .ZDE | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZDI | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZEB | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZFSENDTOTA | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZGF | Safe Software | Ikke Almindelige Filer | Landmark Zycor Graphics File | FME Desktop | Safe Software |
| .ZGZ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZH3 | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZIQ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZML | Check Point Software Technologies Ltd. | Ikke Almindelige Filer | ZoneAlarm Mailsafe Renamed Data | WinZip | Corel |
| .ZPAR | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZQ2 | ZoneAlarm | Ikke Almindelige Filer | ZoneAlarm Mailsafe File | Mailsafe | ZoneAlarm |
| .ZQ8 | ZoneAlarm | Ikke Almindelige Filer | ZoneAlarm Mailsafe File | Mailsafe | ZoneAlarm |
| .ZQQ | ZoneAlarm | Ikke Almindelige Filer | ZoneAlarm Mailsafe File | Mailsafe | ZoneAlarm |
| .ZR4 | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZS9 | Nintendo | Ikke Almindelige Filer | ZSNES Slot 9 Saved State File | ZSNES | Nintendo |
| .ZUC | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .ZUML | Gentleware AG | Ikke Almindelige Filer | Poseidon For UML Project Information File | Poseidon for UML | Gentleware AG |
| .ZUN | Unknown Developer | Ikke Almindelige Filer | Recogsp File | Unknown Software | Unknown Developer |
| .ZVPL | Visual Paradigm | Ikke Almindelige Filer | Visual Paradigm License File | Visual Paradigm Suite | Visual Paradigm |
| .ZVQ | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
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