The Neurosky Mindset taps into your brainwaves and allows you to watch trippy graphics while you think. It looks more or less like a set of wireless headphones with a theremin attached to it.
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Interestingly, they provide a set of open programming APIs that allow independent developers to more easily create software that interacts with the data coming out of the device. So, although they haven’t created any interesting applications of the device, it’s possible that someone else will.
They seem to be positioning themselves to tap into the burgeoning physical computing scene, by simplifying use of the device in projects involving the Arduino and similar microcontroller devices.
Someone from my grad school has already started working on it.
See also Emotive Epoc for similar device.