KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
GNU Octave - GNU Octave is a programming language for scientific computing.
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
LabVIEW - LabVIEW offers many of the functions you'd find in a traditional script-based programming language presented in a more intuitive visual interface ideal fo engineering.
QUCS - Qucs, briefly for Quite Universal Circuit Simulator, is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming