| xss | Dataset Designer Surface Data |
| xst | IBM WebSphere Query Template |
| xsym | CodeWarrior xSYM File |
| xtml | XML4web HTML Document |
| xul | XML User Interface Language File |
| y | Yacc Source |
| yab | Yabasic Source Code |
| yac | Yacc Source |
| yacc | Yacc Source |
| ymx | Yukes 3D Object |
| yobj | Yukes 3D Object |
| ysp | BYOB Sprite |
| yy | GNU Bison Parser |
| zcos | Scilab XML Diagram |
| zef | Unity Pro Full Application Exchange File |
| zem | Zope External Editor File |
| zep | Zephir Source Code |
| zexp | Zope Binary Export File |
| zf3d | Flare3D Model |
| zfd | ABC Zeroadic Functions Data |
| zh | Netscape Navigator Java Classes File |
| zog | Zoggy Data |
| zpd | ABC Zeroadic Predicate Data |
| zpk | Zend Studio Application Package |
| zrp | RapidPLUS Application Package |
| zsf | Zend Server Exported Events |
| zsh | Z-Shell Script |
| zsm | ZSM Assembler Source Code |
| ztk | Zope Toolkit Data |
| zul | ZK User Interface Layout |
| zup | Microsoft Dynamics NAV Development Environment Setup Parameters |
