https://www.kicad.org/discover/spice/
SPICE Simulation | KiCad
KiCad integrates the open source spice simulator ngspice to provide simulation capability in graphical form through integration with the Schematic Editor.
spice simulationkicad
https://cswspiceopustap.liber3.eth.limo/
Circuit Simulation with SPICE OPUS: Theory and Practice - Tadej Tuma, Árpád Buermen (auth.) - pdf
circuitsimulationspiceopustheory