| .S1H | Oracle Corporation | Webfiler | Sealed HTML Document | Unknown Software | Unknown Developer |
| .S1Y | Yamaha Corporation | Lydfiler | Yamaha EX-series Synthesizer Internal Voice And Performance Data | Unknown Software | Unknown Developer |
| .S2 | Motorola | Datafiler | Motorola S-record Format | Unknown Software | Unknown Developer |
| .S4T | i4i, Inc | Datafiler | S4/TEXT And Tagless Editor Data | Unknown Software | Unknown Developer |
| .SAC | Adobe Systems Incorporated | Ikke Almindelige Filer | Shared Asset Catalog File | Unknown Software | Unknown Developer |
| .SAF | DeLorme | GIS-filer | Street Atlas USA Map File | Unknown Software | Unknown Developer |
| .SAG | Sagem Communication (SAFRAN Group) | Lydfiler | Sagem Ringtone Format | Unknown Software | Unknown Developer |
| .SAIF | Safe Software | Grafiske Filer | Spatial Archive Interchange Format | Unknown Software | Unknown Developer |
| .SAMPLE | Unknown Developer | Datafiler | Saved Sample | Unknown Software | Unknown Developer |
| .SASF | NASA | Udviklerfiler | NASA Spacecraft Activity Sequence | Unknown Software | Unknown Developer |
| .SBWMM | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SC$ | Unknown Developer | Ikke Almindelige Filer | Modem Bitware Fax Disk1 Files | Unknown Software | Unknown Developer |
| .SC2 | EA Maxis | Spilfiler | SimCity 2000 City File | Unknown Software | Unknown Developer |
| .SC? | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SCAN | Unknown Developer | 3D-billedfiler | Scan Data | Unknown Software | Unknown Developer |
| .SCANNER | Unknown Developer | Rasterbilledfiler | Scanner Output File | Unknown Software | Unknown Developer |
| .SCHDOCPREV | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SCPS | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SCX | RIX SoftWorks, Inc. | Rasterbilledfiler | ColoRIX Bitmap Graphic File | Unknown Software | Unknown Developer |
| .SDR | Dell Boomi | Ikke Almindelige Filer | Dell Support File | Unknown Software | Unknown Developer |
| .SDU | Edwards Systems Technology, Inc. | Datafiler | Edwards Systems Technology File | Unknown Software | Unknown Developer |
| .SEB | Franklin Electronic Publishers, Inc. | eBogsfiler | Franklin eBookMan E-book | Unknown Software | Unknown Developer |
| .SECF | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SEG | SEG (The Society of Exploration Geophysicists) | Datafiler | SEG-2 Data File | Unknown Software | Unknown Developer |
| .SERIAL | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SEU | Unknown Developer | Ikke Almindelige Filer | Serials 2000 Encrypted S2K Update | Unknown Software | Unknown Developer |
| .SFE | Unknown Developer | Systemfiler | Logomatic V2 Firmware | Unknown Software | Unknown Developer |
| .SGB | Relic Entertainment | Spilfiler | Dawn Of War Map File | Unknown Software | Unknown Developer |
| .SGC | Secure Computing (SCC) | Ikke Almindelige Filer | Secure SnapGear Router Configuration | Unknown Software | Unknown Developer |
| .SG_ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SHELL | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SHOP | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SIGNPRO | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SIO | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SIX | Digital Equipment Corporation | Rasterbilledfiler | DEC LN03+ Sixel Bitmap Image File | Unknown Software | Unknown Developer |
| .SLAP | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMART2 | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMH | Oracle Corporation | Tekstfiler | Sealed MHT Document | Unknown Software | Unknown Developer |
| .SML2 | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMN | Unknown Developer | Datafiler | ParaGraph WorkScript Data | Unknown Software | Unknown Developer |
| .SNC | Swiftpage, Inc. | Indstillingsfiler | ACT! E-mail/folder Synchronization File | Unknown Software | Unknown Developer |
| .SND | Open Source | Lydfiler | Sound File | Unknown Software | Unknown Developer |
| .SNF | The Open Group | Skrifttypefiler | UNIX Font | Unknown Software | Unknown Developer |
| .SNIFFER | Unknown Developer | Datafiler | Sniffer Trace File | Unknown Software | Unknown Developer |
| .SOFTWARE | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SOUP | Unknown Developer | Datafiler | Message / E-mail File | Unknown Software | Unknown Developer |
| .SO_ | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SPAM | Unknown Developer | Webfiler | Spam E-mail Message | Unknown Software | Unknown Developer |
| .SPARSE | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SPIFF | Joint Photographic Experts Group | Rasterbilledfiler | Still Picture Interchange File Format | Unknown Software | Unknown Developer |
| .SPRITES | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SRH | BMC | Datafiler | BMC Remedy AR System Server Saved Search | Unknown Software | Unknown Developer |
| .SRO | Unknown Developer | Datafiler | MADCOW Multi-Site ATIS Data Collection Working Group Data | Unknown Software | Unknown Developer |
| .SS2 | Unknown Developer | Datafiler | Terrasoft SAS Program File | Unknown Software | Unknown Developer |
| .SS3 | Unknown Developer | Lydfiler | Singer Song Writer Audio File | Unknown Software | Unknown Developer |
| .SSCA | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SSD??= | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SSTMP | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .STACK | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAGE1 | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAR | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STARTUP | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STDF | Teradyne | Datafiler | Standard Test Data Format | Unknown Software | Unknown Developer |
| .STEGANO | Unknown Developer | Datafiler | Steganographic Image File | Unknown Software | Unknown Developer |
| .STORAGE | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STV | Unknown Developer | Datafiler | SofTV Authoring Data | Unknown Software | Unknown Developer |
| .SU | Unknown Developer | Ikke Almindelige Filer | Country Code Top-level Domain | Unknown Software | Unknown Developer |
| .SVTREPORTER | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SWD_RAP | Unknown Developer | Ikke Almindelige Filer | Unknown File Type | Unknown Software | Unknown Developer |
| .SWR | Unknown Developer | Datafiler | SageWorld Anti-Hacker Program File | Unknown Software | Unknown Developer |
| .SY# | Unknown Developer | Sikkerhedskopifiler | Darn! Backup File | Unknown Software | Unknown Developer |
| .SYMBOLS | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYMLINK | Unknown Developer | Ikke Almindelige Filer | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SYNTAX | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYSLOG | Apple | Datafiler | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .S_S | Unknown Developer | Ikke Almindelige Filer | Eru/erd File | Unknown Software | Unknown Developer |
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