| .XTR | SourceForge | Compressed Files | XTrkCad Demo File | XTrackCAD | SourceForge |
| .XX | Unknown Developer | Compressed Files | XXEncoded File | Corel WinZip 21 | Corel |
| .XXE | Unknown Developer | Compressed Files | XXEncoded File | Corel WinZip 21 | Corel |
| .XXL | Unknown Developer | Compressed Files | File Archive Handler Compressed Archive | File Archive Handler | Unknown Developer |
| .XZ | Various Developers | Compressed Files | XZ Compressed Archive | 7-Zip | Igor Pavlov |
| .Y | Microsoft Corporation | Compressed Files | Subsampled Raw YUV Image | Microsoft Windows Media Player | Microsoft Corporation |
| .YAR | Unknown Developer | Compressed Files | YAK Compressed Archive | Unknown Software | Unknown Developer |
| .YBS | Unknown Developer | Compressed Files | YBS Compressed Archive | YBS | Unknown Developer |
| .YC | Unknown Developer | Compressed Files | YAC Compressed Archive | Unknown Software | Unknown Developer |
| .YN | Unknown Developer | Compressed Files | Audio Utility Tuningwrench Compressed File | Unknown Software | Unknown Developer |
| .YZ | Open Source | Compressed Files | YAC Compressed File | YACC | Open Source |
| .YZ1 | Yamazaki Satoshi | Compressed Files | Yamazaki ZIPPER File | IZArc | Ivan Zahariev |
| .Z | Smith Micro Software | Compressed Files | Unix Compressed File | 7-Zip | Igor Pavlov |
| .Z01 | Corel | Compressed Files | WinZip First Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z02 | Corel | Compressed Files | WinZip Second Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z03 | Corel | Compressed Files | WinZip Third Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z04 | Corel | Compressed Files | WinZip Fourth Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z05 | Corel | Compressed Files | WinZip Fifth Split Zip File | WinZip | Corel |
| .Z06 | Corel | Compressed Files | WinZip Sixth Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z07 | Eugene Roshal | Compressed Files | Split Multi-volume RAR Compressed File | WinZip | Corel |
| .Z08 | Eugene Roshal | Compressed Files | Split Multi-volume RAR Compressed File | WinZip | Corel |
| .Z09 | Eugene Roshal | Compressed Files | Split Multi-volume RAR Compressed File | WinZip | Corel |
| .Z96 | Eugene Roshal | Compressed Files | Split Multi-volume RAR Compressed File | WinZip | Corel |
| .ZAP | Check Point Software Technologies Ltd. | Compressed Files | ZoneAlarm Pro Data File | ZoneAlarm Antivirus | Check Point Software Technologies Ltd. |
| .ZAR | Sony | Compressed Files | PlayStation 2 Audio Data | PlayStation 2 | Sony |
| .ZBA | Open Source | Compressed Files | Compressed Data File | ZipZag | Open Source |
| .ZDB | Synacor Inc. | Compressed Files | Zimbra Database File | Microsoft Outlook | Microsoft Corporation |
| .ZDS | Avery Dennison | Compressed Files | Avery DesignPro Label File | Avery Design & Print | Avery Dennison |
| .ZET | Unknown Developer | Compressed Files | ZET Compressed Archive | Unknown Software | Unknown Developer |
| .ZFC | Alistair George Manufacturing | Compressed Files | Back4Win Backup Archive File | Back4Win | Alistair George Manufacturing |
| .ZFSENDTOTARGET | Microsoft Corporation | Compressed Files | Windows XP ZIP Compressed Folder | WinZip | Corel |
| .ZFX | zipLogix | Compressed Files | ZipForm File | ZipLogix zipForm Standard | zipLogix |
| .ZIP | Winrar | Compressed Files | Zipped File | 7-Zip | Igor Pavlov |
| .ZIP2 | Smith Micro Software | Compressed Files | StuffIt Archive | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .ZIPX | Corel | Compressed Files | Extended Zip File | The Unarchiver | Dag Agren, Circlesoft |
| .ZIX | WinZix Software Developers | Compressed Files | WinZix Compressed File | WinZix | WinZix Software Developers |
| .ZLD | Jean-loup Gailly and Mark Adler | Compressed Files | Zlib Compressed Archive | Zlib | Jean-loup Gailly and Mark Adler |
| .ZLG | Open Source | Compressed Files | E-Surveiller Log Archive File | e-Surveiller | Open Source |
| .ZLIB | Jean-loup Gailly and Mark Adler | Compressed Files | Zlib Archive | Zlib | Jean-loup Gailly and Mark Adler |
| .ZOM | Check Point Software Technologies Ltd. | Compressed Files | ZoneAlarm Mailsafe Renamed Data | WinZip | Corel |
| .ZOO | e-merge GmbH | Compressed Files | ZOO Compressed File | WinAce | e-merge GmbH |
| .ZPAQ | Open Source | Compressed Files | ZPAQ Compressed Archive | ZPAQ | Open Source |
| .ZPI | Winrar | Compressed Files | Zipped File | 7-Zip | Igor Pavlov |
| .ZPK | Z-Firm | Compressed Files | Z-Firm Package File | FaxRush | Z-Firm |
| .ZPRF | Tom Brown | Compressed Files | ZipIt Preference Data | ZipIt | Tom Brown |
| .ZPW | Martin Sloup | Compressed Files | ZippedWeb Archive File | ZippedWeb | Martin Sloup |
| .ZW | MYCOLORSCREEN | Compressed Files | Zooper Widget Template | MYCOLORSCREEN Zooper Widget Pro | MYCOLORSCREEN |
| .ZZ | Damien Debin | Compressed Files | Zzip Compressed Archive | Zzip | Damien Debin |
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