Creative Ring

Gimmal ring - Ring made of 2 or 3 hoops that are hinged at the back and meant to interlock and open; popular for betrothals in 16th and 17th century Europe
Iron Ring, a.k.a. Engineer's Ring - Ring worn by American and Canadian engineers, after swearing the Engineer's Oath. This is often in the form of a crudely worked piece of iron; modern rings tend to be sleek steel, some with etched geometric designs. The ring is meant to be worn on the pinky (little) finger of the dominant hand at all times. This ring has been loosely associated with Rudyard Kipling.
Mood ring - A novelty ring which changes color in response to body temperature, using a thermochromic liquid crystal.
Mother's ring - A ring worn by a mother displaying the birthstone of each of her children, and sometimes including those of the mother and father.