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