Our Circuit Design Calculators for Engineers and Students are free-to-use tools that help you quickly determine key parameters ...

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.

We were interested in [Lee Teschler]’s review earlier this year of 30 free circuit simulators. If you are selecting one or don’t like the one you are currently using, it is well worth the time ...