There are a number of devices on the market that can plug into a car's OBD II diagnostic communication port to extract vehicle data. The latest to appear is PLX Devices' Kiwi. Unlike most of the others, which simply display raw mileage data, the Kiwi apparently logs a variety of vehicle information such as throttle and brake data. It uses this in combination with the mileage info to analyze your driving style and give you advice on how to get the most out of a gallon of fuel. It also includes a "Drive Green" mode with some lessons and challenges to test your driving and help you learn more efficient techniques. The cellphone-sized device is currently available for $299, but that introductory price is a limited-time deal and it'll eventually rise to $399. Check out the video after the jump.