R

R is a free, open source software program for statistical analysis, based on the S language. 

RStudio is an IDE (integrated development environment) for R. R must be installed first. RStudio lets you view graphs, data tables, R code and output simultaneously. It also lets you import CSV, Excel, SAS (.sas7bdat), SPSS (.sav)  and Stata (.dta) files without having to write extra code.

• Available for Windows, Macintosh and Linux
• Publication-quality graphs
• Packages for literate statistical programming - weaving written reports and analysis code in one document