Low-Cost Tablet Runs on Three Watts of Power

Marc Mertens, the CEO of Seso, designed the I-slate interface. The challenge, he says, has been to figure out "what is the ideal way to work with students, while making sure the device does as little as it can." That approach keeps hardware costs and power consumption low. Animations and other complex, media-rich tools are just not possible. The math program is based on the standard textbook used in the region and allows students to move at their own pace. They can skip problems if they get stuck. Teachers can download information from each student's device to monitor their progress.
Low-Cost Tablet Runs on Three Watts of Power - Technology Review

This is what I would consider a real computer. It has limited features but it does what it should do really well and really cheaply. It uses no power. The little solar panel doesn't count. But a real benchmark is that it beats books. We had never seen that before.