This is just a binary dump of an R workspace, so it could contain anything (arrays, functions, classed-objects, pointers ...) - you don't want a reader for that. (An equivalent would be to ask for a .mat (Matlab workspace dump) reader and I don't think that's compelling.)
I'd load it in R and explore the objects and use standard write functions to export (contact me off list if you want) probably you want the raster/sf packages for raster/vector data write facilities.
In GDAL-speak this is an R Object Data Store, and this will read (some) array/matrix forms: http://gdal.org/frmt_r.html - this would probably do what you need without using R.
Not to be confused with the raster package's native binary format, which GDAL also reads: http://gdal.org/frmt_various.html#RRASTER