Take a look at Seeeduino XIAO. What a small size and cutelooking! It is the smallest member of the Seeeduino family. SeeeduinoXIAO still carries the powerful CPU-ARM Cortex-M0+(SAMD21G18) which is alow-power Arduino microcontroller.
On the other hand, this little board has good performance in processing but needs less power.
The interfaces of Seeeduino XIAO is rich enough in such a tiny Dev. Board as well.