Tom Gerhardt's mud computer, one of the projects on display at NYU's ITP spring show 2009, is a keyboard replacement made entirely of the squishy stuff. According to Gerhardt, the Mud Tub pioneers a "new open-ended interaction typology where prescriptive goals are centered around states, rather than specific user manipulation". So, for example, instead of clicking "Send" on your email, the Mud Tub might ask you to move two fingers a certain way in the mud.
It's hard to imagine a situation where the Mud Tub would be more useful than a traditional keyboard. Gizmodo suggests that the mud UI could assist designers in modeling buildings, car fenders, and other physical objects. But could the mud hold position long enough to create a model of anything substantial? Regardless, Gerhardt's Mud Tub proves that we can connect computers to nature in a very real way.