| sll | PowerBASIC Static Link Library |
| slm | Microsoft Source Library Management File |
| sln | Microsoft Visual Studio Solution |
| slp | Adobe RoboHelp Screen Layout Page |
| slz | Adobe RoboHelp Exported Screen Layout |
| sm2 | Crestron SIMPL Program Backup |
| smali | Android Smali Assembly Source Code |
| smap | JSP Source Map File |
| smcl | Stata SMCL Log |
| smdl | Microsoft SQL Server SMDL Data |
| smft | Crestron SIMPL Autoupdate Manifest Data |
| smpi | LINDO SMPI File |
| smps | LINDO SMPS File |
| smrc | Smtools Repository Data |
| smw | Crestron SIMPL Program |
| sni | MDK Archive |
| snippet | Visual Studio IntelliSense Code Snippet |
| snk | .NET Strong Name Key |
| sno | Snobol4 Language Source Code |
| snw | Sweave Document |
| so | Unix Shared Library |
| soy | Google Closure Template |
| sp2 | SAS Permanent Utility |
| sp45 | SuperCard Player File |
| sp7 | SAS Permanent Utility |
| sparql | SPARQL Script |
| spdslog | SAS Scalable Performance Data Server Log |
| spec | RPM Package Specification |
| spk | Novell Netware Server Source Package |
| spkg | Windows Phone Driver Package |