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.
Circuit Tree - Design and order Boards in Minutes
Circuit Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.
Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.
CircuitLab - Sketch, simulate, and share your circuits, entirely in your browser -- no install required.
Oregano - oregano - An electrical engineering tool for GNOME