Files that contain the .r file extension are most commonly associated with the Mac OS X operating system.
The R files that are used by the Mac OS system contain resource files that are referenced by applications which are run in the Mac OS X environment. These files store the shortcut functions and variable definitions for the associated software applications.
The RatFor Fortran software application has also been known to use the .r file suffix. These R files contain pre-processor source files that are created within the RatFor Fortran program.
The popular Pegasus Mail email application also uses the .r file extension. These R files contain resource files that are references by the email program.
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If you have additional information about the R file format or software that uses files with the R suffix, please do get in touch - we would love hearing from you.