Sweet relaxation. Just in time for the Holidays. 
I custom designed these relaxation stones (worry stones) for my wife and printed them on my printers at 0.05mm layer height to produce a very smooth surface straight off the printer. A little polishing with 800 grit sandpaper and they buff right up smooth and silky.
She loves them and thought my friends here might enjoy them as well.
In the picture below the blue one is polished and the others are raw. Harder plastics like PLA seem to produce a better feel than softer ones.
The files are available here: