Ngspice
Ngspice is a mixed-level/mixed-signal circuit simulator. Its code is based on three open source software packages: Spice3f5, Cider1b1 and Xspice. The simulator is GPL licensed and runs on most platforms. It is shipped as source code, but there are binary packages for Microsoft Windows and it is included in some Linux distributions. If it is shipped with your distribution the shipped macros will run without any adjustments. Also it will run on Windows without adjustment, if you uncompress it in the same folder lever like your LayoutEditor installation (see below). Please check the file permissions, if you install it in the 'Program Files' folder. In all other cases you need to adjust the macro to your installation path. Three macro for ngspice are shipped: trigger the simulation with wave form viewer, trigger the simulation with text output and view only the ngspice netlist. You will find these macros at the menu item Simulation of the SchematicEditor.