| sy7 | Synchro Studio 7 Output Data |
| syc | Network Associates Sniffer Capture |
| sycw | Essential Studio Widgets Data |
| syd | SYSTAT Data File |
| sydb | Syncfusion Essential Studio Database |
| sydw | Essential Studio Dashboard Data |
| syg | SYSTAT Graph |
| syk | Symbolic Link Spreadsheet |
| syl | Symbolic Link Spreadsheet |
| sylk | Symbolic Link Spreadsheet |
| sym | VariCAD Symbol Library |
| symbols | Debian Package Extended Shared Library Information Data |
| symcache | Microsoft Windows Symbol Cache |
| syn | Adobe RoboHelp Synonym List |
| syn | Concordance Synonyms Data |
| syn | COREX Syntactic Annotation Data |
| syn | COREX Syntactic Annotations |
| syn | TextPad Syntax File |
| sync | Apple ColorSync Data |
| syncconflict | iTunes Synchronization Conflict 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 |
