The Button Size Node 3 is a low cost wireless Arduino IDE compatible (the Atmel ATMega328P 8MHz) microcontroller with LoRa RFM 95 or RFM 69 HW(CW) radio on board and few other nice additions.
Best sutable for Home Automation, IOT. Could be used as core board for radio controlling any DIY project. You may think of it as Arduino Pro Mini with Hope RF, light sensor, temperature and humidity sensors, on-board storage, and an Atmel crypto authentication unit on board.

Very tiny - 45mm x 23mm in size.