Colorful weaves of anodized aluminum rings -- smooth, cool, and lightweight. Different configurations allow for multiple fidgeting styles and means of stimulation, and lobster clasps mean you can attach them to zipper pulls, purse rings, keychains, bags, and whatever else you carry with you daily.
The large Fugue fidget is the largest one I make, with a diameter of 3.5" (9cm), and is composed of a total of 164 individually-placed rings (54 large and 110 small). As you can imagine, this takes a while to make, but it's really lovely to fidget with when it's done!
About the name: A fugue (pronounced "fyoog") is "a composition in which a short melody or phrase (the subject) is introduced by one part and successively taken up by others and developed by interweaving the parts." (Bach's Toccata and Fugue in d Minor is the spooky organ one you've definitely heard.) This design begins with a simple Celtic flower design at its center, and is worked outwards in a similar, though not identical, fashion.