As far as I've seen, none of the open source spice tools support more advanced simulation types like periodic steady state, or did I just not look well enough? I'm interested in working on stuff like that, but at this point I just need to study all the bits a lot more. Would be very unfortunate to write such a thing for Xyce and not have it upstream, or contribute to ngspice when it turns out there are better simulators.

Ngspice supposedly has PSS but in development phase. Xyce has harmonic balance. But I haven't used either so idea how good the implementations are