A few years ago, I came across a booth (I believe at a Renaissance Faire) selling the object I've dubbed a "Fidget Widget." You can fidget with it in one or both hands to achieve an effect similar to squeezing a stress ball or twirling a pen in your hand, with the additional perk of an almost hypnotic effect to watch in your hand. (You can watch a GIF of it spinning at http://gph.is/1rimn5R.) After carrying it around in my bag for several years, several friends asked me about it in the same day and inspired me to make my own version of it. I modeled it that night and learned to 3D print within the next week.
The piece consists of six identical links that snap together. The original consisted of three black and three white pieces, and I have tended to prefer the two-color alternating pattern of assembly. I have included examples of other configurations above, but I've been able to mix and match the links at will. The attached STL file is one link. (Please let me know if you attempt to print a full Fidget Widget with all six pieces already assembled in one print or if you try printing in metal, resin, or other non-FDM printers. I'd like to know how it works.)
I've printed on both the Makerbot Replicator 2X in ABS and the Dremel 3D20 in PLA, and I have found the texture and fit of the PLA prints more pleasant in my hand. Friends have preferred the feel of PLA, so either is fine to print with, but my personal preference is ABS. I have done prints with both rafts and supports on and off, though I have noticed no significant differences in quality. The only noted difference between having and lacking supports is in the capped hole section, the bottom side of which dips down somewhat and becomes slightly stringy but is not visible when the full piece is assembled.
After printing, I sometimes file down the interfaces to ensure smoother rotation. Especially when printing PLA, I have noticed rubbing and squeaking when rotating the piece. Filing the groove has generally worked better than trying to evenly file the entire outer surface of the circle and the flat surfaces, as long as you're careful not to damage the circles at the end that snap the pieces together. I have yet to try using acetone or other finishing techniques and would be interested to hear how they work if someone tries them.