Today we made two copies of AmazingSpanoMan's Customizable Fidget Ring on Thingiverse. The center ring spins around very nicely.
STL file: http://www.geekhaus.com/makerhome/day102_fidgetrings.stl
Thingiverse link: http://www.thingiverse.com/thing:188275 (customize your own!)
Stuff to change: The size I printed is a bit too big for me to wear, but still fun to play with. Next time I'll print one that is a bit smaller.