Academics in general, and mathematicians in particular, depend on Free software in their work. A good case can be made that proprietary software is contrary to the academic ethic. Issues of access aside, if one does not know what exactly went into a program, then one cannot fully trust the results that come out, any more than one can trust (for purposes of scientific publication) results of a commercial testing lab. Access to the source code is not all that is required, though. To promote the dissemination of information, users should be granted the four freedoms laid out in the GNU General Public License:
Free0: To run a program for any purpose
Free1: To study how the program works, and adapt it to your needs
Free2: To redistribute copies of the program
Free3: To improve the program, and release improvements to the public
Just as theorems are not restrictively licensed, I believe that software we use in our academic work should be licensed in a way that encourages openness and sharing. Releasing software under a standard commercial license agreement is (to me) the equivalent of publishing the statement of a theorem, while keeping the proof secret, and charging people for each citation of the theorem. Releasing source code alone, without giving users the freedom to modify it for their own needs, is analogous to publishing a proof, but forbidding readers from using the ideas of the proof in their own work.
The ultimate purpose of software is to allow us to be productive and creative. I hope that this modest program is, in conjunction with the much larger efforts of others (especially Donald Knuth, Richard Stallman, and the many people who have contributed to the authorship of LATEX and its packages), useful to you in your mathematical work.
Please visit the Free Software Foundation, at
http://www.fsf.org, to learn more about Free Software and how
you can contribute to its development and adoption.