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 Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.

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.

KiCad - A Cross Platform and Open Source Electronics Design Automation Suite

Circuit Solver - Circuit Solver uses a simple drag and drop approach to building circuits.

LibrePCB - LibrePCB is a free EDA software to develop printed circuit boards.