VoltSim is described as 'Interactive realtime circuit simulator. It has digital and analog components and even Integrated Circuits. It the perfect companion to students, hobbyists, and engineers' and is a circuit simulator in the education & reference category. There are nine alternatives to VoltSim for a variety of platforms, including Mac, Windows, Android, iPhone and Windows Phone apps. The best VoltSim alternative is Circuit JS, which is both free and Open Source. Other great apps like VoltSim are LTspice, CircuitJS1 Desktop Mod, Everycircuit and iCircuit.