That’s the reason for the vast versions of SPICE available now decades after the original was released, not all of which are as open or free as we might like. Qucs is a GPL circuit simulator.

This project report presents an LT SPICE simulation. LT SPICE is a SPICE-based analog electronic circuit simulator computer software, produced by semiconductor manufacturer Analog Device. It is the ...

[Mike] is the developer responsible for LTSpice, which is quite likely the most widely used spice-compatible simulator in the free software ... LTSpice is your best friend. And, like all best ...