| .SLAP | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMART2 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMH | Oracle Corporation | File di testo | Sealed MHT Document | Unknown Software | Unknown Developer |
| .SML2 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SMN | Unknown Developer | File di dati | ParaGraph WorkScript Data | Unknown Software | Unknown Developer |
| .SNC | Swiftpage, Inc. | File di settaggi | ACT! E-mail/folder Synchronization File | Unknown Software | Unknown Developer |
| .SND | Open Source | File audio | Sound File | Unknown Software | Unknown Developer |
| .SNF | The Open Group | File di font | UNIX Font | Unknown Software | Unknown Developer |
| .SNIFFER | Unknown Developer | File di dati | Sniffer Trace File | Unknown Software | Unknown Developer |
| .SOFTWARE | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SOUP | Unknown Developer | File di dati | Message / E-mail File | Unknown Software | Unknown Developer |
| .SO_ | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SP2 | Amusement Vision (SEGA) | File di giochi | Super Ball 2 Level File | Super Ball 2 | Unknown Developer |
| .SPAM | Unknown Developer | File web | Spam E-mail Message | Unknown Software | Unknown Developer |
| .SPARSE | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SPIFF | Joint Photographic Experts Group | File con immagini raster | Still Picture Interchange File Format | Unknown Software | Unknown Developer |
| .SPRITES | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SRH | BMC | File di dati | BMC Remedy AR System Server Saved Search | Unknown Software | Unknown Developer |
| .SRO | Unknown Developer | File di dati | MADCOW Multi-Site ATIS Data Collection Working Group Data | Unknown Software | Unknown Developer |
| .SS2 | Unknown Developer | File di dati | Terrasoft SAS Program File | Unknown Software | Unknown Developer |
| .SS3 | Unknown Developer | File audio | Singer Song Writer Audio File | Unknown Software | Unknown Developer |
| .SSCA | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SSD??= | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SSTMP | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SSY | Unknown Developer | File compressi | ScreenShare Compressed Data | ScreenShare | Unknown Developer |
| .STACK | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAGE1 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STAR | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STARTUP | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STDF | Teradyne | File di dati | Standard Test Data Format | Unknown Software | Unknown Developer |
| .STEGANO | Unknown Developer | File di dati | Steganographic Image File | Unknown Software | Unknown Developer |
| .STORAGE | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .STS | DuoS DSEMU | File di giochi | DuoS DSEMU Saved State File | DuoS DSEMU | Unknown Developer |
| .STV | Unknown Developer | File di dati | SofTV Authoring Data | Unknown Software | Unknown Developer |
| .SU | Unknown Developer | File vari | Country Code Top-level Domain | Unknown Software | Unknown Developer |
| .SUL | Unknown Developer | File con immagini raster | GFA Raytrace Image | GFA Raytrace | Unknown Developer |
| .SVTREPORTER | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SWD_RAP | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .SWR | Unknown Developer | File di dati | SageWorld Anti-Hacker Program File | Unknown Software | Unknown Developer |
| .SXT | FMJ-Software | File audio | Propellerheads Reason 2 NN-XT Sound Data | Formula Graphics | Unknown Developer |
| .SY# | Unknown Developer | File backup | Darn! Backup File | Unknown Software | Unknown Developer |
| .SYMBOLS | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYMLINK | Unknown Developer | File vari | Uncommon File Extension | Unknown Software | Unknown Developer |
| .SYNTAX | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SYSLOG | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .SZS | Nintendo | File di dati | Wii Game Data File | CTools | Unknown Developer |
| .S_S | Unknown Developer | File vari | Eru/erd File | Unknown Software | Unknown Developer |
| .T04 | Tobias Svensson | File 3D | Top 4 Compressed Data File | top 4 | Unknown Developer |
| .TABLE1 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TABLES | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TAL | Adobe Systems Incorporated | File di testo | Adobe TypeAlign Text Illustration File | Unknown Software | Unknown Developer |
| .TALK | Unknown Developer | File di dati | Text To Speech File | Unknown Software | Unknown Developer |
| .TALK2 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TASP | Unknown Developer | File di giochi | Strategy Planner Data File | Tactical Assault Strategy Planner | Unknown Developer |
| .TCO | Unknown Developer | File di dati | T9000 Object Module | Unknown Software | Unknown Developer |
| .TDR | PO KSI | File backup | ArVid Tape Backup | Top Draw | Unknown Developer |
| .TDT | Sony | File video | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TEASERS2 | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEBK | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .TECH | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEK | Unknown Developer | File di dati | ASITIC Technology File | ASITIC | Unknown Developer |
| .TELL | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TEMP | Safer Networking Ltd. | File vari | Temporary (Temp) File | Original Program That Created The File | Unknown Developer |
| .TEST | Unknown Developer | File di dati | Testing File | Unknown Software | Unknown Developer |
| .TESTING | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TFB | Unknown Developer | File vari | Unknown Apple II Data File | Unknown Software | Unknown Developer |
| .TFR | LucasArts Entertainment Company, LLC | File di giochi | TIE Fighter Pilot File | Unknown Software | Unknown Developer |
| .TG1 | Unknown Developer | File vari | On Target Project File | Unknown Software | Unknown Developer |
| .TGR | The U.S. Census Bureau | File di GIS | Tiger Line Data | Unknown Software | Unknown Developer |
| .THML | Unknown Developer | File sviluppatore | Theological HTML Document | Theological Markup Language (ThML) | Unknown Developer |
| .THW | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .TICKET | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TID | Sony | File video | AVCHD Thumbnail File | Unknown Software | Unknown Developer |
| .TIK | Unknown Developer | File sviluppatore | Script File For Game Textures | Unknown Software | Unknown Developer |
| .TILE | XnSoft | File con immagini raster | Eclipse Image | Unknown Software | Unknown Developer |
| .TIPS | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TJL | Unknown Developer | File backup | VAXTPU Editor Backup File | Unknown Software | Unknown Developer |
| .TJT | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .TJZ | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .TKI | Unknown Developer | File vari | Mime: Application/x-tkined | Unknown Software | Unknown Developer |
| .TNL | Unknown Developer | File 3D | Thumbnail Image Format | Unknown Software | Unknown Developer |
| .TO | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TOAD | Unknown Developer | File vari | FunkyToad System File | FunkyToad Network | Unknown Developer |
| .TRACKS | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRANSFERIR | Unknown Developer | File vari | Unknown File Type | Unknown Software | Unknown Developer |
| .TRAVEL | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRD | Marco Pontello | File di dati | TrID Definitions Package | TR Assistant | Unknown Developer |
| .TRIAL | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TRIF | Tiling Task Group (TTG) | File con immagini raster | Tiled Raster Interchange Format | Unknown Software | Unknown Developer |
| .TRUETYPE | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TSH | CENiX, Inc. | File audio | Cenix Audio | Unknown Software | Unknown Developer |
| .TTO | Unknown Developer | File vari | Client Access Data Specification File | Unknown Software | Unknown Developer |
| .TTS | SumTotal Systems | File di dati | ToolBook Translation System File | TrueTime | Unknown Developer |
| .TVLINK | Unknown Developer | File vari | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TVW | Unknown Developer | File vari | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TVX | Doug Cutting | File vari | Apache Lucene Term Vector Index File | Unknown Software | Unknown Developer |
| .TVZ | Unknown Developer | File vari | Uncommon File Extension | Unknown Software | Unknown Developer |
| .TWN | Unknown Developer | File di settaggi | Scanner Settings File | Unknown Software | Unknown Developer |
| .TWO | Apple | File di dati | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .TXG | ESRI | File vari | Georeference Subobject File | Unknown Software | Unknown Developer |
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