[j_b_s]

Nope! Base R works great. Old-school vi to edit scripts, and R base installation to run them (or REPL around). Of course, the IDEs do offer a lot of support, and RStudio is great for making your R functions into packages that are easy to share.

[_Wintermute]

That was in reference to the rstudioapi package for finding the path of the current file, which I've just checked out needs a running Rstudio session to work.