The AAduino Zero (blog post) is the successor of the AAduino and is still the same size as an AA battery. This repo contains software for the AAduino Zero and will eventually hold the hardware schematics.

There's lots of example code available, and a simple serial tool for flashing these.

• STM32L052 micro controller with 32kb flash, 8kb RAM, 2kB EEPROM
• RFM68CW radio module
• TMP102 temperature sensor
• 4Mbit serial flash for sensor data logging and wireless firmware upgrades
• 32kHz oscillator for RTC
• Activity LED
• Reverse polarity protection
• 1x digital/analog I/O port
• UART port on 0.1” header
• Pre-programmed with a serial boot loader capable of handling firmware upgrades via radio or the UART.
• Minimum supply voltage: 1.8V
• Maximum supply voltage: 3.6V
• Minimum power consumption: 8μA. Yes, eight microamps.