The little gold ones are "miniatures", made for jewellery purposes. You can find them in the form of several different kinds of famous world coins. The two top ones at least are probably made of 8k gold.
The tiny cent was indeed part of a set. THey were often sold as a novelty labelled "worlds smallest coins", though of course they're not real official coins.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
By law, copies my be > twice as big as a large dollar, or < half as small as a dime or be marked "copy". Beyond that, anyone can make them. I've seen them marked Nixon money, Carter money, inflation money, etc.