The ATTO measures just 10.3 x 11.5 mm² and weighs 0.68 g. Nionics has equipped the board with an Atmel ATmega32U4 microcontroller, a micro USB port and a reset button. The company has pre-flashed the board with the Arduino Leonardo bootloader too. The ATTO is available to pre-order now for US$11.90 and will ship worldwide in October.
https://www.notebookcheck.net/Nionics-ATTO-The-world-s-smallest-Arduino-board-is-available-to-pre-order-for-under-US-12.422959.0.html