| swq | SWAT Stream Water Quality Input Data |
| swr | SageWorld Anti-Hacker Program Output |
| swsd | Sodera Spectrum Data |
| swstd | SolidWorks Design Checker Data |
| swv | Sidewinder Game Voice Settings |
| swzk | SWiSH Wizard Data |
| sxcmp | SIMetrix Components Data |
| sxdat | SIMetrix Data |
| sxg | Stradx Segmentation Data |
| sxgph | SIMetrix Graph Binary Data |
| sxr | Stradx Registration Data |
| sxs | Str3Di Data |
| sxsch | SIMetrix Schematic Data |
| sxsnp | SIMetrix Snapshot Data |
| sxt | Formula Graphics Script |
| sxv | Action Repeater File |
| sxv4 | SuperSTAR Database |
| sy | Simplexety Data File |
| sy1 | AMI Pro Smartpix Symbol Library |
| 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 |
| syncml | Open Mobile Alliance SyncML Data |
| syr | Xilinx XST Synthesis Report |
| sys | General Swap File |
| sys | Microsoft SQL Server Data Replication System Table Data |
| syx | MIDI System Exclusive Message |
| syz | SYSTAT Data |