| SD | Sound Designer I Audio |
| SD2 | Sound Designer 2 Flattened File / Data Fork |
| SD2 | SAS Database |
| SDA | StarOffice Drawing |
| SDA | PGP Encrypted Executable |
| SDA | SoftCuisine Data Archive |
| SDB | SideKick 2 Database |
| SDC | StarOffice Spreadsheet |
| SDD | StarOffice Presentation |
| SDE | Drumbeat (Internet application) Exported Data |
| SDF | System Data File Format - Legacy Unisys (Sperry) Format |
| SDF | Autodesk MapGuide Spatial Data Files |
| SDG | Star Office Gallery |
| SDI | QuickBooks Data |
| SDK | Roland S-series Floppy Disk Image |
| SDK | Autosketch Drawing |
| SDL | SmartDraw Library |
| SDL | Inprise (Borland) Delphi Sound Library |
| SDN | Shell Archive |
| SDP | IBM Storyboard PIC Image |
| SDP | QuickTime Session Description Protocol File |
| SDP | Real Player File |
| SDR | SmartDraw Drawing |
| SDS | Raw Midi Sample Dump Standard File |
| SDS | StarOffice Chart |
| SDT | QuickBooks Data |
| SDT | SmartDraw Template |
| SDT | Archive (various games) |
| SDV | Semicolon Divided Values File |
| SDW | Lotus WordPro Graphic File |
| SDW | Raw Signed DWord (32bit) Data |
| SDW | SourceSafe Files in Shadow Directory |
| SDW | StarOffice Text |
| SDX | Midi Sample Dump Standard Files Compacted by SDX |
| SEA | Stuff-it Self-expanding Archive |
| SEC | PGP Secret Key Ring |
| SEC | Compressed Archive File |
| SEG | Compressed File Segment |
| SEL | PaintShop Pro Selection File |
| SEP | TIFF Bitmap Separation |
| SEQ | Animation File |
| SEQ | Chromeleon Sequence List |
| SEQ | Guillomet Maxi Home Studio II |
| SES | Cood Edit Session File |
| SET | Backup File Set for Microsoft Backup |
| SET | Driver Set (various) |
| SET | Image Settings (various) |
| SET | Configuration (various) |
| SEX | Urban Chaos Game File |
| SF | IRCAM SoundFile Format |
| SF | OS/2 WPS Attribute Storage |
| SF2 | Emu SoundFont v2.0 File |
| SF2 | Creative Labs Soundfont 2.0 Bank File |
| SFD | SoundStage Sound File Data |
| SFE | Split Files Shell Extension |
| SFI | SIS Frame Grabber |
| SFI | Ventura Publisher Printer Font |
| SFI | SoundStage Sound File Info |
| SFL | Ventura Printer Font |
| SFL | LaserJet Landscape Font |
| SFN | Font (various) |
| SFP | LaserJet Portrait Font |
| SFP | Ventura Printer Font |
| SFR | Sonic Foundry Sample Resource |
| SFS | PCL 5 Scalable Font |
| SFS | StarOffice Frame |
| SFT | StarOffice Frame |
| SFT | Chiwriter Screen Font |
| SFW | Seattle Film Works (Mangled JPEG) |
| SFX | Sound Effects for Games |
| SFX | RAR Self-extracting Archive |
| SG1 | Stanford Graphics |
| SGF | Star Writer Document |
| SGF | Smart Game Format |
| SGI | IRIS, Silicon Graphics Image |
| SGL | StarOffice Master Document |
| SGM | SGML Structured Generalized Markup Language |
| SGN | Sierra Print Artist Sign |
| SGO | IRIS Inventor Nodes |
| SGP | Stat Graphics Plus |
| SGT | DirectMusic Producer |
| SH | UNIX Shell Script |
| SH3 | Harvard Graphics for DOS 3.0 Presentation |
| SHA | UNIX SHAR Archive |
| SHB | Document Shortcut File |
| SHB | Corel Background File |
| SHB | Shell Scrap object |
| SHD | Print Spooler Shadow File |
| SHG | Hotspot Editor Hypergraphic |
| SHH | Automated Setup Template |
| SHK | Shrink-it for Apple Macintosh Archive |
| SHM | WordPerfect Shell Macro |
| SHP | 3D Studio Shapes File |
| SHR | Archive File |
| SHS | Shell Scrap Object File |
| SHT | Structured HTML |
| SHTML | HTML file that supports Server Side Includes(SSI) |
| SHW | Corel Show Presentation |
| SHW | Harvard Graphics DOS 2.x Show |
| SHW | WordPerfect Slide Show |
| SHX | AutoCAD Shape |
| SI | SoftImage Image File |
| SIB | Sibelius Music File |
| SID | Mr SID Compressed Raster Image |
| SIF | Windows NT Setup File |
| SIF | Autodesk Spatial Index File |
| SIG | Signature File (various) |
| SIG | Print Shop Sign File |
| SIK | Backup File |
| SIM | Intel VTune performance monitor |
| SIM | Simulation (various) |
| SIM | PowerDVD File |
| SIS | SymbianOS Installer File |
| SIT | Stuffit Macintosh Compressed Archive File |
| SIZ | Oracle 7 Configuration |
| SJF | Split Files Shell Extension |
| SKA | PGP Secret Keyring |
| SKB | QuickPOS (Point-Of-Sale) Standard Keyboard Layout File |
| SKC | SKCARD SideKick for Windows |
| SKL | Macromedia Director Resource File |
| SKN | FileWrangler/SecurDesk!/ImageForge Graphic Skin |
| SKN | eRocket eBook Skin |
| SKN | The Sims (Maxis) 3D Body Mesh Skin Data |
| SKR | Microsoft ScriptIt |
| SKW | SKWRITE SideKick Write or Calendar |
| SKY | ActiveSky Movie Clips for Palm OS |
| SL | PACT's Save Layout |
| SL | S-Lang Program File |
| SLB | AutoDesk Slide Library File Format |
| SLC | Telix Compiler SALT Script |
| SLD | AutoDesk Slide File Format |
| SLG | Chromeleon Audit Trail |
| SLI | MAGICorp Slide Image |
| SLK | Symbolic Link (SYLK) Spreadsheet |
| SLM | Microsoft Visual FoxPro |
| SLT | Telix SALT Script Application |
| SM | Samna Word Text File |
| SM | SMALLTALK Source Code |
| SM | Soft Spoken Mailer |
| SM3 | DataCAD Symbol File |
| SMC | Lotus Freelance Graphics Smart Master Content |
| SMD | StarOffice Mail |
| SMD | SEGA mega drive ROM file |
| SMF | Smart-Fax Document |
| SMF | StarOffice Formula |
| SMI | Lotus Smart Suite Smart-icon |
| SMI | RealPlay SMIL File |
| SMK | Smacker Compressed File |
| SML | Simple Markup Language |
| SMM | WordPro/AmiPro Macro |
| SMP | Samplevision Format |
| SMP | Ad Lib Gold Sample |
| SMP | PhotoImpact Gallery File |
| SMS | MS Package Definition File |
| SMT | Quick Books |
| SMT | HiPer-Six Memo File |