| sitv | StuffIt Viewer Data |
| siw | ANSYS SIwave Data |
| sjd | Scrapbook Factory Journal Data |
| sjf | SCAPS SAM JobFile Format |
| sjx | Seljax Estimating and 3D Design Data |
| sk | Safari History Index |
| ska | PGP Secret Keyring Data |
| skba | Autodesk SketchBook Pro Animation File |
| skc | SideKick Card |
| skcard | Borland Sidekick Card File |
| skel | Geomview OOGL Objects SKEL Data |
| skim | Skim Notes File |
| skindex | Apple Mail Index Data |
| skl | Autodesk Maya Skeleton Works Data |
| sklib | Skatter Library Data |
| skn | Windows Automotive Skin |
| skpkmz | SketchUp Data |
| skr | Gaussian Scratch File |
| skr | PGP Private Keyring File |
| skypechatstyle | Skype Chat Style Data |
| skypeemoticonset | Skype Emoticon Pack |
| sl | RenderMan Shader Source |
| sl2 | Lowrance Sonar Log v2 File |
| sl3 | SQLite 3 Database |
| slb | Multiframe Sections Library |
| slc | SLiCe Format Data |
| sldasm | SolidWorks Assembly Document |
| sldblk | SolidWorks Blocks File |
| sldbombt | SolidWorks BOM Template |
| sldclr | SolidWorks Color Palette Data |
| sldd | Simulink Data Dictionary |
| slddc | Simulink Data Dictionary Cache |
| sldedb | SolidWorks Database |
| sldftp | SolidWorks Form Tool File |
| sldholtbt | SolidWorks Hole Table Template |