The ubiquitous iPad is well known because the primary interface is, well, your finger. Sometimes more than one. Nevertheless, a new iPad app promises to turn the tables on the interface by permitting you to design (with your trusty iPad finger) a 3D ring. The iRing3D app by Paracloud does just that.
The app lets you select an initial design from a group of typical ring shapes, after which you may play with the design (with your finger) to adjust the shape as you like. There's plenty of options for customization.
While that's mildly interesting, it gets better: once you've completed your design you can upload your jewelry design directly from the iPad to 3D print services Shapeways or Sculpteo! Then the ring you designed will be produced in real life, hopefully in solid gold or some such valuable metal, and you'll soon have a real ring around the same finger that designed it.