Free electronic circuit simulators.

The following free circuit simulators are available from electronic component manufacturers.

And these free simulators are not from component manufacturers.

Two of them, that is NGspice/Kicad, and QUCS, are available under a GPL (General Public license), they have been developed by a group of people rather than a commercial company. Note that I have not listed any simulators which you have to buy, or simulators that are not freely available to the amateur community.