URL: https://www.r-project.org/

Licence: Free, and distributed under the terms of the GNU General Public License

R is a free, open source programming language and software environment for statistical analysis and graphics. 

The R programming language is highly extensible and provides a wide variety of functions that support linear modeling, non-linear modeling, classical statistics, classifications, clustering and more. Also, R has an active community of users online where one can turn to for support.