| xmss | FileMaker Pro XML Script |
| xmwx | ExamSoft SofTest Working Data |
| xnk | Microsoft Exchange Public Folder Shortcut |
| xpt | Mozilla Firefox XPCOM Type Library |
| xrnx | Renoise Tool |
| xrs | Real Player External Resource |
| xslic | XenServer License Data |
| xtea | XTEA Encyrpted Data |
| xtn | OSLib Program |
| xtnd | Adobe Acrobat for Mac Plug-in |
| xtra | Adobe Director Xtra Extension |
| xuv | BlueFlash Firmware Image |
| xxc | Centraline COACH Controller Firmware |
| xxe_addon | XMLmind XML Editor Add-on |
| ybd | YobiDrive Link |
| yenc | yEnc Encoded File |
| ymp | YaST Meta Package |
| ync | yEnc Encoded File |
| yti | Google Picasa Plugin |
| yxwz | Alteryx Designer Analytic App |
| z0 | ZoneAlarm MailSafe Renamed JS File |
| z1 | ZoneAlarm MailSafe Renamed VB File |
| zex | ZOOM MRS-802 System File |
| zfsendto | Windows Compressed Folder Shortcut |
| zg | Honeywell MP Compact4 Firmware |
| zgi | Zoomerang Web Survey Page |
| zgk | ZIPGenius Key Data |
| zipenx | Egis Encrypted Data |
| zl0 | ZoneAlarm MailSafe Renamed ADE File |
| zl1 | ZoneAlarm MailSafe Renamed ADP File |