LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.

Pspice - OrCAD PSpice technology provides the best, high-performance circuit simulation to analyze and refine your circuits, components, and parameters before committing to layout and fabrication

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.

Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.

PyLab_Works - PyLab_Works is a free and open source replacement for LabView + MatLab, written in pure Python.

Oregano - oregano - An electrical engineering tool for GNOME