Called Zoomboard, the idea is that a small screen can contain a full QWERTY keyboard by smartly zooming as you type. Press down on part of the keyboard, and it zooms to show keys in just that area; pressing again types a letter. It also uses swipes to help you edit: swipe right to insert a space, left to delete, or up to see symbols.
It's not a complicated bit of technology, but it's neatly executed and could at least allow you to type a short message on your wrist. It better be short, though: in tests, students managed a fairly paltry 9.3 words per minute on the keyboard.
But that's OK, because this is a first step. Smart watches won't be perfect at first, but it's nice to know that people are at least thinking about how to make them work. The software will be presented at the Computer Human Interaction conference in Paris this week, and the source code will be made freely available, too. More here.