R - your flexible friend!
it is...
- software for statistical computing and graphics
- free (GNU General Public Licence) implementation of the S programming language
- named partly after the creators (Ross Ihaka and Robert Gentleman) and in reference to S
- related to the commercial S implementation S-PLUS
- based on a command line interface (various GUIs are available though)
- extensible through loadable libraries
- availabe for multiple platforms incl. UNIX, *BSD, Linux, MacOS, Windows
- well documented with its own documentation format, similar to UNIX man pages
- complex, nothing you master over a coffee break