Scilab
Octave
FreeMat
JMathLib - A Java Clone of Octave, SciLab and Matlab
Mathnium - A System for Numerical Computing, Data Analysis, and Graphics
TeLa
Algae
Lush (Lisp Universal SHell)
Yorick
Rlab
Maxima
Sage: open source mathematics software
Euler
S-Lang library
Python
with NumPy
and SciPy
The R Project for Statistical Computing (not a clone, but same matrix multiplication plus more)
Matlab Clones
Matlab Clones & Portation
Alternatives to Matlab
ehrhardt@math.tu-berlin.de