KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Circuit Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.
Altium Designer - PCB Design Software
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.
Autodesk EAGLE - Autodesk EAGLE is an electronic design automation (EDA) software.
Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.