LTSpice
From Steak Wiki
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).
Guaranteed to Work on Linux (TM)
For 32 bit linux, use LTSpice XVII.