File extensions that begin with X, Y or Z.

 Ext.  Type of file
 XAR   Xara drawing

 XBM   X Window bitmap

 XFX   JetFax

 XLA   Excel add-in
 XLAM  Excel add-in (Open XML)
 XLB   Excel toolbar
 XLC   Excel chart
 XLD   Excel dialogue
 XLK   Excel backup
 XLM   Excel macro
 XLS   Excel spreadsheet
 XLSB  Excel 2007 spreadsheet fast binary format
 XLSM  Excel macro (Open XML)
 XLSX  Excel spreadsheet (Open XML)
 XLT   Excel template
 XLTM  Excel template and macro (Open XML)
 XLTX  Excel template (Open XML)
 XLW   Excel project

 XML   XML file

 XPI   Firefox extension (cross Platform Install)
 XPM   X Window pixelmap

 XSD   W3C XML Schema
 XSL   XML Style sheet

 XWD   X Window dump

 XY?   XyWrite document (?=version)
 XYW   XyWrite for Windows document

 Z     gzip archive

 ZBD   Canon image backup

 ZIP   PKZIP compressed

 ZOO   Zoo compressed

 $$$   Temporary