| sxv | Action Repeater File |
| sxv4 | SuperSTAR Database |
| sxy | Spike2 XY Views Data |
| sy | Simplexety Data File |
| sy0 | WordExpress Data |
| sy1 | AMI Pro Smartpix Symbol Library |
| sy7 | Synchro Studio 7 Output Data |
| syc | Network Associates Sniffer Capture |
| syd | SYSTAT Data File |
| syg | SYSTAT Graph |
| syl | Symbolic Link Spreadsheet |
| sylk | Symbolic Link Spreadsheet |
| sym | VariCAD Symbol Library |
| symbols | Debian Package Extended Shared Library Information Data |
| syn | TextPad Syntax File |
| sync | Apple ColorSync Data |
| syncdb | iTunes Sync Database |
| synciddb | SQLite Data |
| syncml | Open Mobile Alliance SyncML Data |
| synctex | SyncTeX Data |
| syo | SYSTAT Output Data |
| syr | Xilinx XST Synthesis Report |
| sys | General Swap File |
| sys | Microsoft SQL Server Data Replication System Table Data |
| sysex | MIDI System Exclusive Message |
| syx | MIDI System Exclusive Message |
| syz | SYSTAT Data |
| sy_ | Compressed SYS File |
| sz | WinAMP Skin |
| sz3 | Scream Tracker 3 Data |
