Generate diagrams to create electronic circuits. That is the main purpose of qucs, a free tool that is developed under the GPL license, with which you'll be capable of carrying out all kinds of different simulations.
Among the kinds of simulations compatible with Quite Universal Circuit Simulator you'll find DC, AC, S Parameter, analysis of the harmonics or noise balance, digital simulation... Thus, you'll be able to simulate the behavior of any circuit.
Quite Universal Circuit Simulator for PC
The developers have also added Qucsator to the product, a command-line terminal circuit simulator that you can use both in the application or as a totally independent program. With Qucsator you'll be able to use a file as the data input to be used in the application or to obtain a file from a data pack that has been processed by the program. Furthermore, qucs is totally free.
You can download qucs and start enjoying all the options that it offers you to design electronic circuits, qucs for Windows is one of the best alternatives for this kind of task.