Per http://www.scilab.org/products/scilab/license 

Scilab 5 is governed by the CeCILL license (GPL compatible) abiding by the rules of distribution of free software.
See the information delivered on the Free Software Foundation on CeCILL >>

You can use, modify and/or redistribute the software under the terms of the CeCILL license as circulated by CEA, CNRS and INRIA at the following URL: http://www.cecill.info

< The English version, CeCILL Free Software License Agreement  v1.1, is at http://www.cecill.info/licences.en.html >