R is a language and environment for statistical computing and graphics.
R is available as Free Software. You can download R using this link
The RStudio integrated development environment (IDE) is a separate piece of software that works with R to make it much more user friendly and also adds some helpful features.
You can download R Studio here:
R for Data Science by 
R in Action by 
Understanding and Applying Basic Statistical Methods Using R by 
R for Political Data Science by 
Data Science in Education Using R by 
Reproducible Econometrics Using R by 
Text Mining with R by The UCLA's Advanced Research Computing R Guide contains tutorials and useful resources to learn R
R-bloggers. You will find posts, news and tutorials on R.
Analytics Using R. Textbook by Margie Rosenberg from the Wisconsin School of Business that covers the major features of R.
Quick-R. A clear and well-organized R tutorial
You can visit deisdata.github.io for asynchronous materials on R, and other software