Mac simulators

[Plinio Andres Barraza]

The recent thread about virtual syths contains alot of good information,
but  I think what the original post was seeking (im not sure) is a program
that simulates circuits, like spice, which could be like a virtual
breadboard for beginners that will play the sound that the circuit
generates.  I have access to a mac and I am looking for something similar
that I can download from the web... for free?  

Im sure this has been covered, but any suggestions as to where to look
would be greatly apreciated.  

Plinio Barraza
synth builder wannabe