Though tangential to your request, I'd point out that there are some
simulators that are good for specific problems. RFSim99, for example,
is a wonderfully simple and useful little program for looking at linear
RF circuits. It includes a Butterworth and Chebychev filter design
tool, attenuator design, L/pi/T match tool, inductor, capacitor,
transmission line, splitter, and coupler tools, and an L/C/f/X
calculator, in addition to the circuit simulation/two-port network
analysis in the main window.

Cheers,
Tom