Johan Kanflo has a new project posted the AAduino, that is available on Github:
The AAduino is an wireless Arduino clone the size of an AA battery with Keystone battery terminals rotated 180° to act as positive and negative terminals. It is powered by an ATMega328p and is fitted with an RFM69C companion. There is room for two DS18B20 temperature sensors and an indicator LED.
Project info at Johan Kanflo’s blog.