| yss | YcySoft Screen Saver Producer Data |
| ytdl | youtube-dl Downloaded Fragment |
| ytf | YTGen Population Data |
| ytm | YTGen Method Data |
| ytp | madVR Test Pattern |
| ytr | IRIS OCR Data |
| yum | YUM Data |
| yumtx | YUM Transaction Data |
| yves | YVES Bible Plugin Data |
| ywl | YoWindow Landscape Data |
| z1 | Z-machine Z-code File |
| z2 | Z-machine Z-code File |
| z3 | Z-machine Z-code File |
| z3l | ZW3D Part Library |
| z4 | Z-machine Z-code File |
| z5 | Z-machine Z-code File |
| z6 | Z-machine Z-code File |
| z64 | N64 ROM Image Mr. Backup Z64 |
| z7 | Z-machine Z-code File |
| z8 | Z-machine Z-code File |
| z80 | ZX Spectrum Emulator Snapshot Z80 |
| zak | Carlson Survey Coordinate Data |
| zam | ZTreeWin ZTreeWin Application Menu Data |
| zapc | ArcSoft Print Creations |
| zar | Zemax Archive |
| zargo | ArgoUML Model Data |
| zav | MT-Card Saved Game Data |
| zbb | Zemax Black Box Data |
| zbd | Canon ZoomBrowser EX Database |
| zbf | Radiance Z-buffer File |
| zbf | Zemax Beam File |
| zbin | Report Server Localization Data |
| zblorb | Z-machine Package |
| zbp | Boardmaker Compressed Package |
| zcast | Creative ZENcast Organizer Data |