GNU Octave
The Octave syntax is largely compatible with Matlab. The Octave interpreter can be run in GUI mode, as a console, or invoked as part of a shell script. More Octave examples can be found in the Octave wiki.
GNU Octave can be extended by packages. Find them at:
Octave is free software licensed under the GNU General Public License (GPL). Assuming you have Mercurial installed on your machine you may obtain the latest development version of Octave sources with the following command:
hg clone https://hg.octave.org/octave