Circuit JS is described as 'This is a javascript electronic circuit simulator. When the applet starts up you will see an animated schematic of a simple LRC circuit. The green color indicates positive voltage. The gray color indicates ground. A red color indicates negative voltage' and is a popular circuit simulator in the education & reference category. There are more than 25 alternatives to Circuit JS for a variety of platforms, including Windows, Linux, Mac, Web-based and Android apps. The best Circuit JS alternative is QUCS, which is both free and Open Source. Other great apps like Circuit JS are LTspice, Multisim, SimulIDE and CircuitLab.