Google Android Device Kit
The Android Open Accessory initiative and the Google Android Device Kit, is built on the open-source Arduino. It lets developers create their own hardware accessories that can be controlled by Android. The base board itself is an Arduino Mega 2560 with USB Host shield, pretty much identical to the official Arduino ADK board.
A limited number of kits were produced and distributed at the Google I/O 2011 developer conference. However, many hardware builders have reproduced and enhanced the original design and these boards are available for purchase. The following list of distributors are currently producing Android Open Accessory compatible development boards:
The Arduino Store provides the Arduino Mega ADK (for EU nations or non- EU nations) that is based on the ATmega2560 and supports the ADK firmware.
DIY Drones provides an Arduino-compatible board geared towards RC (radio controlled) and UAV (unmanned aerial vehicle) enthusiasts.
mbed provides a microcontroller and a library to develop accessories that support the Android accessory protocol.
Microchip provides a PIC based USB microcontroller board.
Modern Device provides an Arduino-compatible board that supports the ADK firmware.
RT Corp provides an Arduino-compatible board based on the Android ADK board design.
Seeed Studio provides an Arduino-compatible board that supports the ADK firmware.
SparkFun's IOIO board now has beta support for the ADK firmware.
Troido has produced an Arduino-compatible version of the ADK hardware
The Accessory Demo Shield sits on top, and provides the following:
tri-color LEDs (3)
Servo controls (2)
Capacitive touch sensor
Joystick (X,Y, and push-switch)