Defpom's CB Radio Simulator for Mac

From S&M Software:

This programme allows you to select a preset PLL type and it shows you what its circuitry layout and what the various internal frequencies are for each channel, also gives you the ability to simulate frequency conversion, so you can test it without having to do it on a real CB radio, you can also select your own crystal frequencies and PLL "N" codes for testing expansion ideas.

It also makes a good trouble shooting tool, as it tells you what the internal frequencies should be for a given PLL type, so you are able to see if a frequency is incorrect or missing, very handy for those unknown radios that use a generic design, it can tell you any frequency that the radio is capable of producing from its PLL "N" code range or loop frequency.