So the Accessory Development Kit from Google is open-source and based on Arduino, as opposed to the one from Apple which is closed-source, NDA, sign your life to Apple. Here you are.
also das Accessory Development Kit (ADK) ist Open Source und basiert auf Arduino, im Gegensatz zu dem von Apple, das Closed Source ist,  Verschwiegenheitsvertrag, "Melde dein Leben bei Apple an". Hier, bitte sehr!