| File extension | Developer/Producer | File description |
|---|---|---|
| Y file extension | N/A | Amiga Yabba Compressed Archive Format |
| Y01 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y02 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y03 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y04 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y05 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y06 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y07 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y08 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y09 file extension | Corel Corporation | Corel Paradox Secondary Index |
| Y3A file extension | Konami | Yu-Gi-Oh! Online Avatar Format |
| Y3D file extension | Konami | Yu-Gi-Oh! Online Card Format |
| Y3P file extension | Konami Corporation | Yu-Gi-Oh! Online Profile |
| Y3T file extension | Konami Corporation | Yu-Gi-Oh! Online Tag |
| Y4M file extension | N/A | YUV4MPEG2 Video Format |
| Y8PD file extension | Spotmau Corporation | Password Finder Yahoo! Mail / Yahoo! Messenger Exported Password |
| YAB file extension | Yabasic | Yabasic Source Code |
| YADPCM file extension | N/A | Raw Yamaha 4-bit ADPCM Format |
| YAH file extension | CousySoft | HeartBeat |
| YAJL file extension | lloyd | YAJL Script |
| YAK file extension | Blue Heron Kayaks | KayakFoundry 3D Design |
| YAL file extension | Arts and Letters | Arts & Letters Clipart Library Format |
| YAM file extension | N/A | Yahoo! Auctions Data Format |
| YAML file extension | N/A | YAML Document |
| YAODL file extension | Silicon Graphics | Powerflip 3D Image Format |
| YAR file extension | Hitachi | StarBoard Document |
| YAST file extension | OpenSUSE | YaST |
| YAWS file extension | N/A | Yaws Source |
| YBC file extension | SUSE | SUSE Linux Enterprise Server Display Settings |
| YBD file extension | EZC Group | YobiDrive Link Format |
| YBHTM file extension | Spacejock Software | YBook HTML |
| YBK file extension | Microsoft | Microsoft Encarta Yearbook Format |
| YBM file extension | Lavasoft | Ad-Aware 2007 |
| YBRAR file extension | Spacejock Software | Ybook Ebook |
| YBRTF file extension | Spacejock Software | Ybook Ebook |
| YBTXT file extension | Spacejock Software | Ybook Ebook |
| YCHAT file extension | Yahoo! | Yahoo! Instant Messenger Chat Log Format |
| YCM file extension | Super Simple Games | Yugioh Card Maker Format |
| YCP file extension | SUSE | SUSE Linux Enterprise Server Display Settings |
| YCT file extension | David Binette | YahELite Chat Transcript |
| YDC file extension | Konami | Konami Yu-Gi-Oh! Card Deck Format |
| YDL file extension | Silicon Graphics | Powerflip YAODL 3D Image Format |
| YDR file extension | Konami | Yu-Gi-Oh! Power Of Chaos Replay Format |
| YDT file extension | Konami | Konami Yu-Gi-Oh! Power Of Chaos Data Format |
| YEL file extension | N/A | Yellow Color Separation |
| YENC file extension | N/A | YEnc Encoded Archive |
| YFS file extension | YSFLIGHT.com | YSFLIGHT Mission Format |
| YG0 file extension | Corel Corporation | Corel Paradox Secondary Index |
| YG1 file extension | Corel Corporation | Corel Paradox Secondary Index |
| YG2 file extension | Corel Corporation | Corel Paradox Secondary Index |
| YG3 file extension | Corel Corporation | Corel Paradox Secondary Index |
| YG4 file extension | Corel Corporation | Corel Paradox Secondary Index |
| YGF file extension | yWorks | YWorks Binary Graph Format |
| YGN file extension | Spacejock Software | YGen |
| YIF file extension | N/A | Mungyodance Game Data |
| YKA file extension | Crocodile Clips | Yenka Model Format |
| YM file extension | Atari | AY-3-8910 Audio Format |
| YMAP file extension | MindGenius Ltd. | MindGenius Computer Aided Thinking Format |
| YMBK file extension | Xilisoft Corporation | Xilisoft Mobile Manager Phonebook |
| YMG file extension | Yahoo! | Yahoo! Messenger Format |
| YML file extension | N/A | YAML Document |
| YML2 file extension | N/A | YML Script Format |
| YMP file extension | YaST | YaST Metapackage Format |
| YNC file extension | N/A | YEnc Encoded Format |
| YOG file extension | Outerra | Outerra Recorded Video Format |
| YOOKOO file extension | Penguin George | Yookoo Player Playlist Format |
| YOS file extension | Hewlett-Packard Company | HP Photosmart Essential Thumbnail Cache |
| YPC file extension | N/A | WhyPic Picture |
| YPF file extension | David Binette | YahELite Configuration |
| YPR file extension | BYOB | BYOB Project Format |
| YPS file extension | Yahoo! | Yahoo! Instant Messenger Format |
| YRCBKM file extension | YRC Group Inc. | YRC Weblink Bookmarks Archive |
| YRM file extension | Electronic Arts, Inc. | Red Alert 2: Yuris Revenge Multiplayer Map |
| YRP file extension | YGOPro Project | YGOPro Replay |
| YSE file extension | Yamaha Corporation | Yamaha Studio Manager Session |
| YSM file extension | Yamaha Corporation | Yamaha Studio Manager |
| YSP file extension | BYOB | BYOB Sprite Format |
| YSS file extension | YcySoft | YcySoft Screen Saver Producer |
| YTF file extension | Google Picasa Font Cache | |
| YTI file extension | Google Inc. | Google Picasa Plugin |
| YTIF file extension | Yellow Tools | Independence Instrument |
| YTR file extension | I.R.I.S. s.a. | I.R.I.S. OCR Data |
| YUV file extension | N/A | YUV 16Bits Image Format |
| YW3 file extension | Spacejock Software | YWriter 3 Project |
| YW4 file extension | Spacejock Software | YWriter 4 Project |
| YW5 file extension | Spacejock Software | YWriter 5 Project |
| YWEMANIFEST file extension | Yahoo, Inc. | Yahoo! Widgets Manifest |
| YWL file extension | Repkasoft | YoWindow Data |
| YWP file extension | Spacejock Software | YWriter 2 Project |
| YZ file extension | YAC | YAC Compressed Archive Format |
| YZ1 file extension | Yamazaki ZIPPER | Yamazaki Zipper Archive |
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