LTSpice

LTSpice is a popular simulation package.

Tips/Techniques

Amp Hour

https://theamphour.com/196-an-interview-with-mike-engelhardt-spice-simulator-synteresis/

Simulating a delay

https://www.youtube.com/watch?v=-aQ77YI7inI A competent user of LTSpice. A good video to show usage and a reasonable circuit as well (the circuit is essentially simulating a 555 timer from discrete (well op amps) components).