MSN: 10 Silly Gingerbread Man Jokes for Kids (+ Free PDF Printables)
I don't think there's any difference in meaning, although "free of charges" is much less common than "free of charge". Regarding your second question about context: given that English normally likes to adopt the shortest phrasing possible, the longer form "free of charge" can be used as a means of drawing attention to the lack of demand for ...
For example, imagine some food company decides to make their fruits permanently free. Online, you can "order" them (for free), but in person, what do you do? What would be the professiona...