LTSpice is a free spice simulator, schematic capture and waveform viewer. LTSpice can be used very well with the LayoutEditor. So circuits create by the SchematicEditor can be used for simulation within LTspice and schematics created by LTspice can be opened, view and used for a schematic driven layer within the SchematicEditor / LayoutEditor. To make the last point working the SchematicEditor must know any symbol used in the schematic. This can be done by importing any symbol into the LayoutEditor. Or more comfortable by using this library which already contains most common symbols used by LTspice.
Using the Library
The LTSpiceLibrary is shipped with the LayoutEditor package and will be installed with it. So no installation is required. The library will be listed within the components libraries. If not, open it by hand. If you open a LTspice schematic any symbol without an explicit given library will be search in this LTSpiceLibrary. If the component was not found, it is search in any opened library. Any missing component can be added with a few clicks via the NewComponent feature. The LTSpice symbol format can be imported within the EditComponent feature.