| str | STELLA Runtime |
| str | STATISTICA Report File |
| string | Zoom Player General Text Data |
| string | UltraEdit String Data |
| strn | HyperCard Stack Converter Data |
| sts | AdriPSX Save State |
| sts | MemMaker Status Information File |
| sts | Nimbus 7 SAMS Status Data |
| stt | Streets & Trips Map Template |
| stv | SofTV Author File |
| stx | SAS XPORT Transport File |
| styk | Stykz Stick Figure |
| stykz | Stykz Animation File |
| styles | Steam Client GUI Resources Data |
| styx | ChordWizard Songtrix Style Data |
| su2 | I2P Software Update File |
| su3 | I2P Software Update File |
| sua | Tim Newport-Peace Special Use Airspace Format File |
| sub | WRAP SIMD Sub-monthly Time Step Simulation Data |
| subs | AvantGo Subscription Data |
| substvar | TIBCO BusinessWorks Substitution Variable Data |
| suc | Softrans Hello Engines! Data |
| sud | I2P Software Update File |
| sud | Super Project Data |
| suf | ZENworks Endpoint Security Management Import File |
| sui | StarSplatter User Interface |
| suite | Theme Manager Data |
| suj | Stacker Unlimited Job |
| sup | Super Project Definition File |
| sup | SOCSIM Supervisory File |
| supf | Egothor Similar Unit Pairs Data |
| sur | Topocad Survey Data |
| surf | V_sim Surface Data |
| sus | SAP Transactionware GM POS Xpress Suspended Data |
| sut | ELITEpro Setup Tables Data |