| extension name | file type | Classification |
|---|---|---|
| YAM | Yahoo! Auctions Data | data file |
| YCHAT | Yahoo! Messenger Chat Log | data file |
| YGF | Y Graph Format File | data file |
| YKA | Yenka Model File | data file |
| YRCBKM | YRC Bookmarks Archive | data file |
| YRCDAT | YRC Software Data Script | data file |
| YUMTX | YUM Transaction File | data file |