See: the zapatistas and revolutionary catalonia for examples of anarchist societies.

You should read about the Frontier days in America after the Louisiana Purchase. Might I suggest the testimony of Dee Harkey?

Harkey continued, “Each person pretty much enforced the laws as he understood them. If the strong imposed his gun on the weak, or became ruthless in his dealings with his fellow man, there was always the posse.”

Were the majority of the posses which lynched accused men justified in their actions?

“Regardless of how men are tried, except by God alone, there are possibilities of mistakes. Those people who had to dish out punishment themselves instead of having someone dish it out for them, as is done today after sentence is pronounced, were usually pretty sure of the guilt before the punishment. Naturally, the formed posses were never considered a means to an end. They were just about as unpopular with the law as the lawless.”