| .S12 | Unknown Developer | Nietypowe Pliki | WISO Steuer-Sparbuch 2012 Data | WISO steuer:Sparbuch 2018 | Unknown Developer |
| .S1H | Oracle Corporation | Plik Web | Sealed HTML Document | Unknown Software | Unknown Developer |
| .S1Y | Yamaha Corporation | Pliki audio | Yamaha EX-series Synthesizer Internal Voice And Performance Data | Unknown Software | Unknown Developer |
| .S2 | Motorola | Pliki z danymi | Motorola S-record Format | Unknown Software | Unknown Developer |
| .S2R | Unknown Developer | Pliki z danymi | RegMagik File | RegMagik | Unknown Developer |
| .S4T | i4i, Inc | Pliki z danymi | S4/TEXT And Tagless Editor Data | Unknown Software | Unknown Developer |
| .SAC | Adobe Systems Incorporated | Nietypowe Pliki | Shared Asset Catalog File | Unknown Software | Unknown Developer |
| .SAF | DeLorme | Pliki GIS | Street Atlas USA Map File | Unknown Software | Unknown Developer |
| .SAG | Sagem Communication (SAFRAN Group) | Pliki audio | Sagem Ringtone Format | Unknown Software | Unknown Developer |
| .SAIF | Safe Software | Pliki graficzny | Spatial Archive Interchange Format | Unknown Software | Unknown Developer |
| .SAMPLE | Unknown Developer | Pliki z danymi | Saved Sample | Unknown Software | Unknown Developer |
| .SASF | NASA | Pliki wydawcy | NASA Spacecraft Activity Sequence | Unknown Software | Unknown Developer |
| .SBE | Safer Networking Ltd. | Pliki konfiguracyjne | Spybot Exclude Data | Safeboot | Unknown Developer |
| .SBF | Google | Pliki systemowe | Android System File | SBF Parser | Unknown Developer |
| .SBWMM | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SC$ | Unknown Developer | Nietypowe Pliki | Modem Bitware Fax Disk1 Files | Unknown Software | Unknown Developer |
| .SC2 | EA Maxis | Pliki gier | SimCity 2000 City File | Unknown Software | Unknown Developer |
| .SC? | Unknown Developer | Nietypowe Pliki | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SCAN | Unknown Developer | Pliki z obrazami 3D | Scan Data | Unknown Software | Unknown Developer |
| .SCANNER | Unknown Developer | Pliki z grafiką rasterową | Scanner Output File | Unknown Software | Unknown Developer |
| .SCHDOCPREV | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SCPS | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SCX | RIX SoftWorks, Inc. | Pliki z grafiką rasterową | ColoRIX Bitmap Graphic File | Unknown Software | Unknown Developer |
| .SDR | Dell Boomi | Nietypowe Pliki | Dell Support File | Unknown Software | Unknown Developer |
| .SDS | Oracle Corporation | Pliki z danymi | OpenOffice.org Chart | SDS Apps | Unknown Developer |
| .SDU | Edwards Systems Technology, Inc. | Pliki z danymi | Edwards Systems Technology File | Unknown Software | Unknown Developer |
| .SEB | Franklin Electronic Publishers, Inc. | Pliki eBook | Franklin eBookMan E-book | Unknown Software | Unknown Developer |
| .SECF | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SEG | SEG (The Society of Exploration Geophysicists) | Pliki z danymi | SEG-2 Data File | Unknown Software | Unknown Developer |
| .SERIAL | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SEU | Unknown Developer | Nietypowe Pliki | Serials 2000 Encrypted S2K Update | Unknown Software | Unknown Developer |
| .SFE | Unknown Developer | Pliki systemowe | Logomatic V2 Firmware | Unknown Software | Unknown Developer |
| .SFO | Interscape | Pliki gier | PSP Game Parameters File | PBP Unpacker | Unknown Developer |
| .SGB | Relic Entertainment | Pliki gier | Dawn Of War Map File | Unknown Software | Unknown Developer |
| .SGC | Secure Computing (SCC) | Nietypowe Pliki | Secure SnapGear Router Configuration | Unknown Software | Unknown Developer |
| .SG_ | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SHAR | Unknown Developer | Pliki skompresowane | Unix Shar Archive | shar | Unknown Developer |
| .SHELL | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SHOP | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SIGNPRO | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SIN | Big Huge Games | Pliki gier | Rise Of Nations Campaign Media File | UnSin | Unknown Developer |
| .SIO | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SIX | Digital Equipment Corporation | Pliki z grafiką rasterową | DEC LN03+ Sixel Bitmap Image File | Unknown Software | Unknown Developer |
| .SLAP | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMART2 | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMH | Oracle Corporation | Pliki tekstowe | Sealed MHT Document | Unknown Software | Unknown Developer |
| .SML2 | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMN | Unknown Developer | Pliki z danymi | ParaGraph WorkScript Data | Unknown Software | Unknown Developer |
| .SNC | Swiftpage, Inc. | Pliki konfiguracyjne | ACT! E-mail/folder Synchronization File | Unknown Software | Unknown Developer |
| .SND | Open Source | Pliki audio | Sound File | Unknown Software | Unknown Developer |
| .SNF | The Open Group | Pliki z czcionkami | UNIX Font | Unknown Software | Unknown Developer |
| .SNIFFER | Unknown Developer | Pliki z danymi | Sniffer Trace File | Unknown Software | Unknown Developer |
| .SOFTWARE | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SOUP | Unknown Developer | Pliki z danymi | Message / E-mail File | Unknown Software | Unknown Developer |
| .SO_ | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SP2 | Amusement Vision (SEGA) | Pliki gier | Super Ball 2 Level File | Super Ball 2 | Unknown Developer |
| .SPAM | Unknown Developer | Plik Web | Spam E-mail Message | Unknown Software | Unknown Developer |
| .SPARSE | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SPIFF | Joint Photographic Experts Group | Pliki z grafiką rasterową | Still Picture Interchange File Format | Unknown Software | Unknown Developer |
| .SPRITES | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SRH | BMC | Pliki z danymi | BMC Remedy AR System Server Saved Search | Unknown Software | Unknown Developer |
| .SRO | Unknown Developer | Pliki z danymi | MADCOW Multi-Site ATIS Data Collection Working Group Data | Unknown Software | Unknown Developer |
| .SS2 | Unknown Developer | Pliki z danymi | Terrasoft SAS Program File | Unknown Software | Unknown Developer |
| .SS3 | Unknown Developer | Pliki audio | Singer Song Writer Audio File | Unknown Software | Unknown Developer |
| .SSCA | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SSD??= | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SSTMP | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SSY | Unknown Developer | Pliki skompresowane | ScreenShare Compressed Data | ScreenShare | Unknown Developer |
| .STACK | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAGE1 | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAR | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STARTUP | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STDF | Teradyne | Pliki z danymi | Standard Test Data Format | Unknown Software | Unknown Developer |
| .STEGANO | Unknown Developer | Pliki z danymi | Steganographic Image File | Unknown Software | Unknown Developer |
| .STORAGE | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STS | DuoS DSEMU | Pliki gier | DuoS DSEMU Saved State File | DuoS DSEMU | Unknown Developer |
| .STV | Unknown Developer | Pliki z danymi | SofTV Authoring Data | Unknown Software | Unknown Developer |
| .SU | Unknown Developer | Nietypowe Pliki | Country Code Top-level Domain | Unknown Software | Unknown Developer |
| .SUL | Unknown Developer | Pliki z grafiką rasterową | GFA Raytrace Image | GFA Raytrace | Unknown Developer |
| .SVTREPORTER | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SWD_RAP | Unknown Developer | Nietypowe Pliki | Unknown File Type | Unknown Software | Unknown Developer |
| .SWR | Unknown Developer | Pliki z danymi | SageWorld Anti-Hacker Program File | Unknown Software | Unknown Developer |
| .SXT | FMJ-Software | Pliki audio | Propellerheads Reason 2 NN-XT Sound Data | Formula Graphics | Unknown Developer |
| .SY# | Unknown Developer | Pliki kopii zapasowej | Darn! Backup File | Unknown Software | Unknown Developer |
| .SYMBOLS | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYMLINK | Unknown Developer | Nietypowe Pliki | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SYNTAX | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYSLOG | Apple | Pliki z danymi | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SZS | Nintendo | Pliki z danymi | Wii Game Data File | CTools | Unknown Developer |
| .S_S | Unknown Developer | Nietypowe Pliki | Eru/erd File | Unknown Software | Unknown Developer |
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