Here is how to install R on OSX 10.9 Mavericks as of 2014-06-01T19:29:55-0500:
brew install gcc brew tap homebrew/science brew install R
gcr@orion:~> gcc --version gcc (GCC) 4.8.3 Copyright (C) 2013 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. gcr@orion:~> r --version R version 3.1.0 (2014-04-10) -- "Spring Dance" Copyright (C) 2014 The R Foundation for Statistical Computing Platform: x86_64-apple-darwin13.2.0 (64-bit) R is free software and comes with ABSOLUTELY NO WARRANTY. You are welcome to redistribute it under the terms of the GNU General Public License versions 2 or 3. For more information about these matters see http://www.gnu.org/licenses/.