Project I did last weekend - when the car hits over 5000 RPM, an Initial D or piece of Eurobeat will blast out. Otherwise, you will have calm japanese music playing as you cruise along. It's my first connected car project in 3 years, and definitely the most fun. The Android device is the main logic controller and communicates over bluetooth with an ELM327 microcontroller connected to the car over the ISO 9141-2 protocol.