Freshmeat page: http://freecode.com/projects/mathomatic/
Mathomatic is a free, portable, general-purpose Computer Algebra System (CAS) that can automatically solve, differentiate, simplify, combine, and compare algebraic equations, perform standard, complex number, modular, and polynomial arithmetic, etc. It does some calculus and is very easy to compile, learn, and use. Plotting expressions with gnuplot is also supported.
Mathomatic has been developed since the year 1986. The license was changed to a free software license in the year 2000. Work continues on it to this day. Community involvement is welcome. A free software GUI needs to be written for it, and any errors or inadequacies in the software or documentation need to be reported so they can be fixed. Many times, interesting new ideas from Mathomatic users are implemented right away, with gratitude from both the user and the developer.
License: GNU LGPL version 2.1
This project has the following developers:
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
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If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!