GNU Octave is a high level interpreted language thought for numerical computation. The language itself is quite similar to matlab, so existing programs/scripts should be portable. Here is a bit about the software from the authors themselves:
Just about everyone thinks that the name Octave has something to do with music, but it is actually the name of one of the author’s former professors who wrote a famous textbook on chemical reaction engineering, and who was also well known for his ability to do quick “back of the envelope” calculations. We hope that this software will make it possible for many people to do more ambitious computations just as easily.
Everyone is encouraged to share this software with others under the terms of the GNU General Public License (GPL). You are also encouraged to help make Octave more useful by writing and contributing additional functions for it, and by reporting any problems you may have.