Creating a Segway without a Gyro!
Check out this video about creating a Segway with NXT without using a gyro sensor.
We built a similar in one of our past classes and was really fun (unfortunately we disassembled it before we had this website ready. We will make a new one in the future and post all the details). The light sensor is used to detect if the segway is unbalancing (so changing the measurement of light) and thus making corrective actions.