Adafruit GEMMA M0 - Miniature wearable electronic platform

The Adafruit Gemma M0 is a super small microcontroller board, with just enough built-in to create many simple projects. It may look small and cute: round, about the size of a quarter, with friendly alligator-clip sew pads. But do not be fooled! The Gemma M0 is incredibly powerful! We've taken the same form factor we used for the original ATtiny85-based Gemma and gave it an upgrade. The Gemma M0 has swapped out the lightweight ATtiny85 for a ATSAMD21E18 powerhouse.