The original circuit simulation software ... and is free to use, but binary-only. (Editor’s note: the author was confused between the GPL open-source Qucs and the closed-source, binary-only ...

But if you have a more complicated circuit, or if you need to do response modeling or other math on your design ... a fully featured free and open source circuit simulation software called Qucs ...

Do you need a free PCB design ... of Materials Manager. Is an open source (GPL) software for the creation of electronic schematic diagrams and printed circuit board artwork. It is useful for everybody ...