Kindle is Amazon’s eBook reader. It uses epaper. The difference between it and a normal device is that the words stay on the screen even when the device is “off”. So it only uses power to “change” the page.
It does this with millions of tiny balls, black on one side, white on the other. These rotate independently. The screen is more readable, like a newspaper, uses real light to show the screen, and use a lot less battery.
I think the ultimate devise would be to put a page of epaper on the lid of a thin laptop – like the Macbookair. I mocked it up in Photoshop below. Close the lid – read a book. Open it, use the laptop. Perfect.