| rrh | BlackBerry Resource Header |
| rsc | Pegasus Mail Compiled Resource |
| rsg | SymbianOS Resource Header |
| rsi | Reactis Info File |
| rsl | Robot Scripting Language |
| rsnippet | Rsnippet Data |
| rsp | MSBuild Response File |
| rsrc | Mac OS X Resource Data |
| rsrs | Buddy API Data |
| rt | Apache Jena RDF Thrift Data |
| rtw | Real-Time Workshop File |
| ruby | Ruby Console Application |
| ruf | ProWorx NXT Address Used Tables Reference |
| rul | InstallShield Install Script |
| rule | Visual C++ Project Rules |
| rules | Visual C++ Project Rules |
| rur | RUR-PLE Solution |
| rvb | Rhino 3D Visual Basic Script |
| rvf | RichView Format Data |
| rvr | RapidPLUS Reviewer Application |
| rvt | VersaPro Reference View Table |
| rwplugin | RapidWeaver Plugin |
| rwsnippet | RapidWeaver Snippet File |
| rwstyle | RapidWeaver Style File |
| rwtheme | RapidWeaver Theme File |
| rwx | RenderWare Script |
| rxd | RapidPLUS XML Application File |
| rxml | Roxen Macro Language Document |
| s | Assembly Source Code |
| s5d | STEP 5 Program |
| s5p | STEP 5 Project |
| s62 | Code::Blocks Assembly Source Code |
| s7f | STEP 7 Project |
| s7l | STEP 7 Library Data |
| s7p | STEP 7 Program |