The MATLAB look-alikes are Scilab, Freemat, and Octave.
Scilab is free for Linux, Windows, Mac OS X, BSD
Freemat is Cross-platform (Linux, Mac OS X, Windows)
GNU Octave is also Windows/Linux/Mac
At least some of these have bindings for Python and Perl.
GNU Octave has a huge tool base because of its use in universities and research facilities like CERN
It has a large common ground with Matlab, but has some commands beyond. Similarly, there are some
MATLAB functions that are not in Octave. Simply taking care on these, you can write and save scripts
that run on both. There is an unsupported GUI front-end called "QtOctave". Surviving copies of the GUI
can be found on the internet. Serious users tend not to bother with it, but new users like it.
http://www.gnu.org/software/octave/
FreeMat strives to be compatible with Matlab, but has "nice" features of its own. It seems to run all the scripts
I ever tried.
http://en.wikipedia.org/wiki/FreeMat
http://freemat.sourceforge.net/
Scilab is a competent tool, with a big user base. The serious solver tool is as good as any, and widely used.
It kind of crosses over between MATLAB and NI LabView, except its icons and interface is not as slick,
and is more primitive - but its free. The syntax is similar to MATLAB, and MATLAB code can be converted.
Like Octave, it has some tools of its own. It has its own (somewhat geeky) command strings that control
diagram display colors, fonts, style, etc. but they are extensive in scope.
http://en.wikipedia.org/wiki/Scilab
http://www.scilab.org/