MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
Cisco Packet Tracer - Download Cisco Packet Tracer, an innovative network simulation and visualization tool used by Cisco Networking Academy students and instructors.
GNU Octave - GNU Octave is a programming language for scientific computing.
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.
GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.