multiple independent R sessions in Mac OS X

Thank you for all the suggestions. Here is a brief summary of the possible solutions:

1. Using Terminal: Run: open -n /Applications/RStudio.app in Terminal
2. Install Emacs and ESS which permit multiple sessions
3. Duplicate the entire R.app package by option-dragging (and you can rename the copies)
4. Run multiple rstudio sessions using projects

Opens another instance of an application in OSX:

open -n -a "APPLICATION NAME"

In this case you'd just do:

open -n -a "rstudio"

CNET article source

I use this all the time on Mac OSX to open multiple Rgui sessions (similar to the Rstudio answer above): open -n /Applications/R.app/ You can do this multiple times for as many R sessions as you want.

Another option for RStudio is to right click the RStudio icon of a current session and select "New RStudio Window":