MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
AQUASIM - In order to support environmental scientists in finding an «adequate» model of the system...
GNU Octave - GNU Octave is a programming language for scientific computing.
STOAT - STOAT - a dynamic sewage treatment works modelling package
Wolfram Mathematica - Mathematica has characterized the cutting edge in specialized processing—and gave the chief calculation environment to a large number of pioneers, instructors, understudies, and others around the globe.
Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.