Quite Universal Circuit Simulator (Qucs) is a open source electronics circuit simulator software released under GPL. It gives you the possibility to set up a circuit with a graphical user interface and simulate the large-signal, small-signal and noise behavior of the circuit. Pure digital simulations are also supported using VHDL and/or Verilog. Qucs supports a growing list of analog and digital components as well as SPICE sub-circuits.
There are three ways how you can used Qucs with the LayoutEditor/SchematicEditor:
Qucs has a own schematic capture program and its own storage format. The LayoutEditor can read this file format. For a correct reading of this file any component used in the schematic has to be present in a component library of the LayoutEditor. Some components are built into Qucs. These components are available in the qucs library shipped with the LayoutEditor.
The SchematicEditor can generate a qucs netlist and trigger the simulation with it. This is done with macros. You can call the macros via the simulation menu inside the SchematicEditor. Often the path to your Qucs installation has to be adjusted inside the macros.
The Qucs package includes a bigger package of printed circuit components. These libraries can be used with the SchematicEditor. To do so call the NewComponent feature and press + to show advanced option. With the import icon you can then select and import a component. The layout information/package information has to be added by hand.