Singular is a computer algebra system for polynomial computations, with special emphasis on commutative and non-commutative algebra, algebraic geometry, and singularity theory. It is free and open-source under the GNU General Public Licence (See COPYING).

Installation instructions from source code: https://github.com/Singular/Sources/wiki/Step-by-Step-Installation-Instructions-for-Singular
Homepage: http://www.singular.uni-kl.de/
Source code: https://github.com/Singular/Sources
User Manual: http://www.singular.uni-kl.de/Manual/latest
Bug/Issue-Tracker: http://www.singular.uni-kl.de:8002/trac
Singular Wiki: https://github.com/Singular/Sources/wiki/
Developer and Reference Manual: http://www.singular.uni-kl.de/dox/html