Circuit Tree - Design and order Boards in Minutes
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
CircuitLab - Sketch, simulate, and share your circuits, entirely in your browser -- no install required.
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
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.
Virtual Breadboard - It is a circuit simulator on a virtual breadboard.