| .Q2D | Nervepreserve | Settings Files | Quick 3D Cover Design File | Quick 3D Cover | Nervepreserve |
| .Q5Q | Flaming Pear Software | Settings Files | SuperBladePro Presets File | Adobe Photoshop | Adobe Systems Incorporated |
| .Q9Q | Flaming Pear Software | Settings Files | BladePro Presets File | Adobe Photoshop | Adobe Systems Incorporated |
| .QAG | Symantec Corporation | Settings Files | Norton Desktop Quick Access Group File | Norton Desktop | Symantec Corporation |
| .QAT | Microsoft Corporation | Settings Files | Microsoft Office Quick Access Toolbar File | Microsoft Office | Microsoft Corporation |
| .QBD | Intuit, Inc. | Settings Files | Quicken Keyboard Layout File | Intuit Quicken | Quicken |
| .QBP | Intuit, Inc. | Settings Files | QuickBooks Printer File | Intuit QuickBooks Pro | Intuit, Inc. |
| .QF | Nokia | Settings Files | Nokia (Ovi) Maps Version Data | Microsoft Notepad | Microsoft Corporation |
| .QHC | Digia Oyj | Settings Files | QHC | Qt SDK | The Qt Company |
| .QIP | Ilgam Zyulkorneev | Settings Files | QIP Infium Account File | QIP | Ilgam Zyulkorneev |
| .QMS | Tencent Holdings Limited | Settings Files | QQMusic Skin | QQMusic | Tencent Holdings Limited |
| .QPX | Microsoft Corporation | Settings Files | FoxPro Compiled Query Program | Microsoft Visual FoxPro | Microsoft Corporation |
| .QRC | Quark Software Inc. | Settings Files | QuarkXPress Required Component File | QuarkXPress | Quark Software Inc. |
| .QSF | Qualtrics | Settings Files | Qualtrics Survey File | Qualtrics Survey Solutions (online) | Qualtrics |
| .QSP | Pantaray Research | Settings Files | QSetup Installation Suite Data | QSetup Composer PRO | Pantaray Research |
| .QSS | Digia Oyj | Settings Files | Qt Style Sheet | Microsoft Notepad | Microsoft Corporation |
| .QTF | Ronald E. Mercer | Settings Files | Qtracker Filter File | Qtracker | Ronald E. Mercer |
| .QTP | Apple | Settings Files | QuickTime Preferences File | Apple QuickTime Player | Apple |
| .QTT | Ronald E. Mercer | Settings Files | Qtracker Application Theme | Qtracker | Ronald E. Mercer |
| .QVT | Qlik | Settings Files | QlikView Theme File | QlikTech International QlikView | Qlik |
| .RAD | Reality Pump Studios | Settings Files | Reality Adlib Tracker Module | Adlib Tracker II | Adlib Tracker II |
| .RB | Larian Studios | Settings Files | Divinity: Original Sin Game Data | Divinity: Original Sin | Larian Studios |
| .RB4 | Sarm Software | Settings Files | Resume Builder 4 File | Sarm Resume Builder | Sarm Software |
| .RCF | Rhapsody International | Settings Files | Audiogalaxy Rhapsody Storage File | Rhapsody | Rhapsody International |
| .RCT | Microsoft Corporation | Settings Files | Visual Studio Resource Template | Microsoft Visual Studio | Microsoft Corporation |
| .RDF | Unknown Developer | Settings Files | Resource Description Framework File | Mozilla Firefox | Mozilla |
| .RDG | Microsoft Corporation | Settings Files | Microsoft Remote Desktop Connection Manager Configuration | Microsoft Remote Desktop Connection | Microsoft Corporation |
| .RDI | SAFEJKA S.R.L. | Settings Files | Rohos Disk Image File | Rohos Mini Drive | SAFEJKA S.R.L. |
| .RDO | Xerox | Settings Files | Xerox Rawster Document Object File | Xerox Document Scan and Make Ready | Xerox |
| .RDP | Microsoft Corporation | Settings Files | Remote Desktop Configuration File | Microsoft Remote Desktop Connection | Microsoft Corporation |
| .RDR | Devolutions | Settings Files | Remote Desktop Manager Settings File | Remote Desktop Manager | Devolutions |
| .RDW | Mediachance | Settings Files | Real-DRAW Project File | Real-DRAW | Mediachance |
| .REG | Microsoft Corporation | Settings Files | Registry File | Windows Registry Editor | Microsoft Corporation |
| .REPX | Developer Express Inc | Settings Files | XtraReports Report Definition | XtraReports | Developer Express Inc |
| .RES | Valve | Settings Files | Valve Resource File | Half-Life | Valve |
| .RESMONCFG | Microsoft Corporation | Settings Files | Microsoft Windows Resource Monitor Settings | Microsoft Resource Monitor | Microsoft Corporation |
| .REX | Propellerhead | Settings Files | ReCycle Loop File | Avid Pro Tools | Avid Technology |
| .RFQ | Siber Systems | Settings Files | RoboForm SearchCard File | RoboForm | Siber Systems |
| .RGD | Redbeet Interactive | Settings Files | Raft Saved Game File | Raft | Redbeet Interactive |
| .RKP | Devolutions | Settings Files | RemoteKeys Profile File | Remote Desktop Manager | Devolutions |
| .RLL | Microsoft Corporation | Settings Files | Microsoft Resource Library | Microsoft Visual Studio | Microsoft Corporation |
| .RLS | Nokia | Settings Files | Symbian Localization File | Symbian SDK | Nokia |
| .RML | Autodesk, Inc. | Settings Files | Redline Markup Language File | Volo View | Autodesk, Inc. |
| .RMS | RealNetworks | Settings Files | Secure Real Media File | RealNetworks RealTimes | RealNetworks |
| .RMSKIN | The Rainmeter Team | Settings Files | Rainmeter Skin File | Rainmeter | The Rainmeter Team |
| .RNX | RealNetworks | Settings Files | RealPlayer Settings File | RealPlayer Cloud | RealNetworks |
| .ROS | Jon Taylor | Settings Files | BattleScribe Roster Editor File | BattleScribe | Jon Taylor |
| .RPB | Famatech | Settings Files | Radmin Phonebook File | Radmin | Famatech |
| .RPK | RadLight | Settings Files | RadLight Media Player Skin | RadLight media player | RadLight |
| .RPS | Autodesk, Inc. | Settings Files | 3ds Max Render Preset Settings | Autodesk 3ds Max | Autodesk, Inc. |
| .RPV | RealNetworks | Settings Files | RealPlayer Visualization File | RealPlayer | Realtime Technologies |
| .RRR | Symantec Corporation | Settings Files | Registry Mechanic Backup File | PC Tools Registry Mechanic | Symantec Corporation |
| .RSP | Rockwell Automation Inc. | Settings Files | RSLogix PLC Program File | RSLogix 5 | Rockwell Automation Inc. |
| .RSX | Red Digital Cinema Camera Company | Settings Files | Temporary Red Alert Camera Data | REDCINE-X | Red Digital Cinema Camera Company |
| .RTL | Hewlett-Packard | Settings Files | Raster Transfer Language File | SwiftView | SwiftView, Inc. |
| .RTO | Micro Focus International plc | Settings Files | Rumba File Transfer Profile | Rumba | Micro Focus International plc |
| .RTS | Heaventools Software | Settings Files | Resource Tuner Console Script | Resource Tuner Console | Heaventools Software |
| .RULESET | Microsoft Corporation | Settings Files | Visual Studio Code Analysis Rule Set | Microsoft Visual Studio | Microsoft Corporation |
| .RWF | HingePoint, Inc. | Settings Files | ReFrame Workspace | ReFrame | HingePoint, Inc. |
| .RXML | Roxen Internet Software | Settings Files | Roxen Macro Language Source Code | Sublime Text | Sublime HQ Pty Ltd |
| .RXP | Roxio | Settings Files | Easy CD & DVD Creator 6 Playlist File | Roxio Creator NXT Pro 5 | Roxio |
| .SBE | Safer Networking Ltd. | Settings Files | Spybot Exclude Data | Spybot - Search & Destroy | Safer Networking Ltd. |
| .SBS | Allegorithmic | Settings Files | Substance Package | Substance Designer | Allegorithmic |
| .SBV | Superbase Software | Settings Files | Superbase Form Definition File | Superbase | Papatuo Holdings Ltd |
| .SBX | Dream Design Entertainment Software | Settings Files | GLBasic Shoebox File | GLBasic | Dream Design Entertainment Software |
| .SCH | Autodesk, Inc. | Settings Files | EAGLE Schematics File | Autodesk EAGLE | Autodesk, Inc. |
| .SCHEMAS | Open Source | Settings Files | GConf Schema Definition File | GNU Emacs | GNU Project |
| .SDC | Stardock Corporation | Settings Files | Stardock Central Download Archive | Stardock Central | Stardock Corporation |
| .SDD | Programming Sunrise | Settings Files | Smart Diary Suite Data File | Smart Diary Suite | Programming Sunrise |
| .SDI | Intuit, Inc. | Settings Files | QuickBooks Data File | Intuit QuickBooks Pro | Intuit, Inc. |
| .SDM | Oracle Corporation | Settings Files | StarOffice Mail Message | StarOffice | Oracle Corporation |
| .SED | Microsoft Corporation | Settings Files | IExpress Self Extraction Directive File | Microsoft IExpress Wizard | Microsoft Corporation |
| .SEQU | Adobe Systems Incorporated | Settings Files | Adobe Acrobat Sequence File | Adobe Acrobat DC | Adobe Systems Incorporated |
| .SES | Adobe Systems Incorporated | Settings Files | Audition Session File | Adobe Audition | Adobe Systems Incorporated |
| .SET | Xerox | Settings Files | Document Library Property Set File | Xerox Library Administration Tool | Fuji Xerox |
| .SETTINGCONTENT-MS | Microsoft Corporation | Settings Files | Microsoft Windows 8.1 Configuration Data | Microsoft Windows 8 | Microsoft Corporation |
| .SETTINGS | Microsoft Corporation | Settings Files | Microsoft Visual Studio Settings File | Microsoft Visual Studio | Microsoft Corporation |
| .SFO | Interscape | Settings Files | PSP Game Parameters File | PBP Unpacker | Unknown Developer |
| .SFS | Open Source | Settings Files | Squashfs File Archive | 7-Zip | Igor Pavlov |
| .SG | Unknown Developer | Settings Files | SG-1000 Game ROM File | Kega Fusion | Steve Snake |
| .SGS | Open Source | Settings Files | WinDS PRO Data | WinDS PRO | Open Source |
| .SGT | IBM | Settings Files | SPSS Chart Template File | IBM SPSS | IBM |
| .SHADOW | Neuber Software | Settings Files | FontTwister Shadow File | FontTwister | Neuber Software |
| .SHH | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Shadow/Highlight Settings | Adobe Photoshop CC | Adobe Systems Incorporated |
| .SIF | Microsoft Corporation | Settings Files | Windows Setup Information File | Microsoft Notepad | Microsoft Corporation |
| .SIZ | Oracle Corporation | Settings Files | Oracle 7 Configuration File | Oracle Database | Oracle Corporation |
| .SKI | Motorola | Settings Files | Motorola Phone Skin File | Apache OpenOffice | Apache Software Foundation |
| .SKIN | Microsoft Corporation | Settings Files | ASP.NET Skin File | Microsoft Visual Studio | Microsoft Corporation |
| .SKL | Autodesk, Inc. | Settings Files | Maya Skeleton File | Autodesk Maya | Autodesk, Inc. |
| .SKN | Avant Force | Settings Files | Avant Browser Skin File | Avant Browser | Avant Force |
| .SKP | Trimble Inc. | Settings Files | SketchUp Document | SketchUp | Trimble Inc. |
| .SKZ | SuperKaramba Project | Settings Files | SuperKaramba Theme | SuperKaramba | SuperKaramba Project |
| .SL | SourceForge | Settings Files | Unix Software License File | Vi | SourceForge |
| .SLT | Mozilla | Settings Files | Mozilla User Profile Folder | Mozilla Firefox | Mozilla |
| .SMR | Uberware | Settings Files | Smedge2 Job Settings File | Smedge2 | Uberware |
| .SMS | Sega | Settings Files | Sega Master System ROM | Kega Fusion | Steve Snake |
| .SMT | Intuit, Inc. | Settings Files | QuickBooks Data File | Intuit QuickBooks Pro | Intuit, Inc. |
| .SMX | MakeMusic, Inc. | Settings Files | SmartMusic XML File | SmartMusic | MakeMusic, Inc. |
| .SNC | Swiftpage, Inc. | Settings Files | ACT! E-mail/folder Synchronization File | Act! | Swiftpage, Inc. |
| .SNX | Pi Innovo | Settings Files | PISnoop Workspace File | PiSnoop | Pi Innovo |
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