| .QF | Nokia | Uncommon Files | Nokia (Ovi) Maps Version Data | Microsoft Notepad | Microsoft Corporation |
| .QIZ | MacKichan Software | Uncommon Files | Exam Builder Quiz | Scientific WorkPlace | MacKichan Software |
| .QLGENERATO | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .QLP | Unknown Developer | Uncommon Files | QuickLink Printer Driver | Unknown Software | Unknown Developer |
| .QND | Unknown Developer | Uncommon Files | Cliq Accessories Notepad Data | Unknown Software | Unknown Developer |
| .QNI | Unknown Developer | Uncommon Files | Cliq Accessories Notepad Data | Unknown Software | Unknown Developer |
| .QNM | Tony Browneller | Uncommon Files | High ASCII Quake Name Maker File | Quake Name Maker | Tony Browneller |
| .QNP | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .QNR | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .QNT | Dionex Corporation | Uncommon Files | Chromeleon Quantification Method File | Chromeleon | Dionex Corporation |
| .QPC | Synergy Software | Uncommon Files | KaleidaGraph Plot File | KaleidaGraph | Synergy Software |
| .QPF | Act-3D | Uncommon Files | Quest3D Project File | Quest3D | Act-3D |
| .QRA | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .QRN | Unknown Developer | Uncommon Files | Quarantine File | Unknown Software | Unknown Developer |
| .QRT | Mats Troeng and Jörgen Ohlin | Uncommon Files | QuickRoute Map | QuickRoute | Mats Troeng and Jörgen Ohlin |
| .QS9 | OzWin | Uncommon Files | OzWin CompuServe E-mail | OzWin | Steve Sneed |
| .QSC | Synergy Software | Uncommon Files | Kaleidagraph Script File | KaleidaGraph | Synergy Software |
| .QSM | Intuit, Inc. | Uncommon Files | QuickBooks Statement Wirter Data | Intuit QuickBooks for Mac | Intuit, Inc. |
| .QSXL | Advanced Publishing Systems | Uncommon Files | QuickLayout Session Data | QuickLayout | Advanced Publishing Systems |
| .QSZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .QTW | Unknown Developer | Uncommon Files | Qtext Text Document | Qtext | Unknown Developer |
| .QUA | Avira Operations GmbH & Co. KG. | Uncommon Files | Avira AntiVir Quarantined File | Avira Antivirus Pro 2016 | Avira Operations GmbH & Co. KG. |
| .QVI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .QW | Symantec Corporation | Uncommon Files | Write Program File | Symantec Q&A | Symantec Corporation |
| .QWK | Unknown Developer | Uncommon Files | BBS Archive File | Unknown Software | Unknown Developer |
| .RA1 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RABBIT | Apple | Uncommon Files | Unknown Apple II File (Golden Orchard Apple II CD Rom) | Golden Orchard | DigiSoft Innovations |
| .RADIOREVOL | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RAINDROPPI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RAL | Span Software | Uncommon Files | WinRail Track Design File | WinRail | Span Software |
| .RAMDISK | DigiSoft Innovations | Uncommon Files | An Unknown Apple II File | Golden Orchard | DigiSoft Innovations |
| .RASMOL | Roger Sayle | Uncommon Files | RasMol File | RasMol | SourceForge |
| .RASTERW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RAT | World Wide Web Consortium (W3C) | Uncommon Files | PICS Rating File | Microsoft Notepad | Microsoft Corporation |
| .RAW_PPM | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RAZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RCE | Unknown Developer | Uncommon Files | NTgraph GUI Control 3D File | Unknown Software | Unknown Developer |
| .RCPROFILE | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RCV | Oracle Corporation | Uncommon Files | Oracle Recovery Manager Script | Oracle Database | Oracle Corporation |
| .RDB-SHM | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RDB2 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RDM | Devolutions | Uncommon Files | Remote Desktop Manager Exported Entries | Remote Desktop Manager | Devolutions |
| .REALDOWNLO | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RECOVERYDA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .REFER | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .REGDUMP | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .REI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .REM | BlackBerry | Uncommon Files | BlackBerry Encrypted Data File | Research In Motion BlackBerry Desktop Manager | BlackBerry |
| .REN | Unknown Developer | Uncommon Files | Renamed File | Unknown Software | Unknown Developer |
| .REP?FB_XD_FRAGMENT= | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .REQ | Open Source | Uncommon Files | SSL Certificate Request File | Microsoft Exchange Server | Microsoft Corporation |
| .REQW | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RESONANCEI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RESOURCESC | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RETURNTOOL | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RFB | Siber Systems | Uncommon Files | RoboForm Bookmark File | RoboForm | Siber Systems |
| .RFC1896 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RFP | Siber Systems | Uncommon Files | RoboForm Passcard File | RoboForm | Siber Systems |
| .RFT | Autodesk, Inc. | Uncommon Files | Revit Family Template File | AutoCAD Architecture | Autodesk, Inc. |
| .RFX | Unknown Developer | Uncommon Files | TouchStar License | Unknown Software | Unknown Developer |
| .RGR | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RHC | RLIB Software | Uncommon Files | ClipX RLIB RHELP Source File | ClipX RLIB RHELP Source File' | RLIB Software |
| .RHT | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RIDEOFVALK | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RII | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RJS | Yukihiro “Matz” Matsumoto | Uncommon Files | Ruby Javascript File | Notepad++ | Don Ho |
| .RKA | Malcolm Taylor | Uncommon Files | RK Audio Compressed Data File | RKau, | Malcolm Taylor |
| .RLA | Wavefront Technologies | Uncommon Files | Alias/Wavefront Image File | XnView MP | XnSoft |
| .RLU | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RMF | Valve | Uncommon Files | Hammer Rich Map Format | Valve Hammer Editor | Valve |
| .RML | Autodesk, Inc. | Uncommon Files | Redline Markup Language File | Volo View | Autodesk, Inc. |
| .RND | Symantec Corporation | Uncommon Files | PGP Random Seed File | Pretty Good Privacy (PGP) | Symantec Corporation |
| .ROADS | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ROM | Various Developers | Uncommon Files | Read Only Memory Image | Basilisk II | Open Source |
| .RPG | Open Source | Uncommon Files | Programming Language Source Code File | RPG Toolkit | Open Source |
| .RPNM | Pierre-Emmanuel Gougelet | Uncommon Files | Portable Image Image File | XnView MP | XnSoft |
| .RPP | Cockos Incorporated | Uncommon Files | REAPER Project | REAPER | Cockos Incorporated |
| .RPSS | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RPST | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RPTDOCUMEN | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RPTTEMPLAT | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RPU | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RQZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RSA | Various Developers | Uncommon Files | RSA Certificate File | Mozilla Firefox | Mozilla |
| .RTC | Brain Innovation | Uncommon Files | BrainVoyager QX Design Matrix File | BrainVoyager QX | Brain Innovation |
| .RTM | Unknown Developer | Uncommon Files | Real Tracker Module | Real Tracker | Unknown Developer |
| .RTP | KTH Royal Institute of Technology | Uncommon Files | Gromacs Residue Topology Parameter File | Gromacs | KTH Royal Institute of Technology |
| .RTX | The Document Foundation | Uncommon Files | Rich Text Document | LibreOffice | The Document Foundation |
| .RU) | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RV2 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .RWJ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .RWZ | Microsoft Corporation | Uncommon Files | Outlook Rules Wizard File | Microsoft Outlook 2016 | Microsoft Corporation |
| .RXC | Sonic Solutions | Uncommon Files | Roxio Certificate File | Roxio Creator NXT Pro 6 | Roxio |
| .RYS | Piotr Fusik | Uncommon Files | Mamut Picture Image File | Recoil | Piotr Fusik |
| .S1 | Open Source | Uncommon Files | Free Pascal File | Free Pascal | Open Source |
| .S12 | Unknown Developer | Uncommon Files | WISO Steuer-Sparbuch 2012 Data | WISO steuer:Sparbuch 2018 | Unknown Developer |
| .S1Q | SealedMedia | Uncommon Files | QuickTime Movie | Sealed | SealedMedia |
| .S7P | Symantec Corporation | Uncommon Files | SubSeven Malware | AVG Antivirus | AVG Technologies |
| .SAC | Adobe Systems Incorporated | Uncommon Files | Shared Asset Catalog File | Unknown Software | Unknown Developer |
| .SBC | Microsoft Corporation | Uncommon Files | Office Accounting Company Shortcut File | Microsoft Office Accounting | Microsoft Corporation |
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