Favorite UI's

Some of the recent discussion in the Savant thread got me thinking. What is your favorite interface, and why? It might be a piece of software you use, a washing machine, your toaster, a web site, a control system you've developed or seen, or your car's media system. We're surrounded by them everywhere and the hardest part is the best ones hardly get noticed - generally thats what makes them good.

For me, I really can't go past the Reactable. The design of the interface makes for an incredible user experience when used for the purpose it was created for - creating. By completely detaching itself from the user experience of a mouse and keyboard computer or a knobs, dials and keys piece of synth hardware it also detaches the users from their pre-determined psycological biases to those interfaces. It sets up a beautiful interaction of objects much in the same way they might be viewed in a visual programming language and allows users to interact with it via physical objects, someone almost the entire human race has a grasp of. It's tactile, fun and does a very good job at putting you in a creative mindset. It truly is an experience.