As posted Freescan is Free. Now Arc-xt and Proscan also work though there is a cost on those. They are all similar, do most of the same things though each has certain bells and whistles that make them unique.
it can even be programmed by hand. for a big system it could be quite the pain, but not too bad.
if you just set up a system and listen you will get to know what you want to pay attention to. after listening to the property appraiser or parking attendant you will realize you might want 10 to 20 groups to listen to and that is all.
in my county my girlfriend listens to about 10 groups.
you can pm back if you have questions.
have fun and enjoy.