R is a statistical analysis and graphics environment that is comparable in scope to the SAS, SPSS, Stata, and S-Plus packages. The basic installation includes all of the most commonly used statistical techniques such as univariate analysis, categorical data analysis, hypothesis tests, generalized linear models, multivariate analysis, and time-series analysis. It also has excellent facilities for producing statistical graphics. Anything not included in the basic installation is usually covered by one of the thousands of add-on packages available.
Because R is command-driven, it can take a little longer to master than point-and-click ...