| yg4 | Corel Paradox Secondary Index |
| yg5 | Corel Paradox Secondary Index |
| yg6 | Corel Paradox Secondary Index |
| ygo | YGOPRO Data |
| yld | SMS Yield Monitor Data |
| yls | YuleLog Data |
| ymbk | Xilisoft Mobile Phone Manager Phonebook Data |
| ymg | Yahoo! Messenger Data |
| yml | YAML Document |
| ymn | Yellicode Modeler Model Data |
| ymt | Yar Material File |
| yob | YASARA Object |
| yos | HP Photosmart Essential Thumbnail Cache |
| ypf | YahElite Personality File |
| ypm | SigmaWinLite Data |
| yps | Yahoo! Messenger YPS Data |
| yrcbck | YRC Weblink Backup Archive |
| yrcbkm | YRC Weblink Bookmarks Archive |
| yrcdat | YRC Weblink Data Script |
| yro | WRAP Yield Versus Reliability Output Data |
| yse | Yamaha Studio Manager Session Data |
| yss | YcySoft Screen Saver Producer Data |
| ysx | Yahoo! Player Stream Description Language 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 |
| yxbe | Alteryx Designer Browse Everywhere Data |
| yxdb | Alteryx Designer Database |
| yxft | Alteryx Designer Field Types Data |