A watch winder, in which the rotational movement is transmitted without contact (with the help of magnets).
Project-Page (German language): http://www.dahlgrimm.de/Arduino/WatchWinder/WatchWinder.html
Also needed (see project-page for the corresponding links to amazon.com):
1x 28BYJ-48 stepper motor
24x Neodym magnet (5x5x5mm)
1x 608 ball-bearing
75mm of a threaded rod (M4)
some screws, washers and a self-locking nut (all in M4)