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, CircuitLab and CircuitJS1 Desktop Mod.