MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
GNU Octave - GNU Octave is a programming language for scientific computing.
C++ - Has imperative, object-oriented and generic programming features, while also providing the facilities for low level memory manipulation
Sage Math - Sage is a free open-source mathematics software system licensed under the GPL.
D (Programming Language) - D is a language with C-like syntax and static typing.
Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.