Recs.
Updated
R is a statistical computing language that runs on many different platforms (Windows, Mac, and Unix/Linux included).
SpecsUpdate
Pros
Pro Lots of packages available
There are lots of different packages available that can be easily searched from the CRAN repo site and downloaded, or installed via the R command line interface. These packages are easy to include in a project or source file, and pertain to a wide variety of topics, from classification, social media analysis, and text processing to interactive 3d plotting and networks (including neural nets).
Pro Has a wide range of options when it comes to IDEs/GUIs
Among the IDEs available there are several commercial applications as well as free and/or open-source ones, such as R Studio, which features syntax highlighting, project management capabilities, integrated terminal access, decent code completion and on-the-spot parameter hinting, graphical interfaces for package installation and such, and commendable extensibility/developer support.