MATLAB - a high-level language of technical calculations, an interactive environment for algorithm development and a modern tool for data analysis.
SpeQ Mathematics
SpeQ is a small royalty-free math program with a simple, intuitive interface. Details can be found on the developer's website.
Cadabra is a computer algebra system
Cadabra is a computer algebra system (CAS) designed specifically for problems arising in field theory. It has extensive functionality for...
QuickMath
QuickMath is another extremely powerful math software on this list, specially designed for teachers and students.