| siqh | Tektronics RSA306 SIQ Header |
| sir | Powersim Studio Simulation Run File |
| sis | Steam Game Backup Info |
| sit | PTC Creo Site Parameter Data |
| sit | Epson Projector Basic Scenario Data |
| site | Sitescooper Sites Data |
| sitf | Seanau Icon Toolkit Data |
| sitl | StuffIt Library Data |
| sito | Stuffit Translator Data |
| sitv | StuffIt Viewer Data |
| siw | ANSYS SIwave Data |
| sj | Google Science Journal 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 |
| skm | SSEYO Koan Data |
| skn | Windows Automotive Skin |
| skpkmz | SketchUp Data |
| skr | Gaussian Scratch File |
| skr | PGP Private Keyring File |