For SAMD21-based boards like the Feather M0, Metro M0, Arduino Zero, and more, we use CircuitPython which is Adafruit's open source derivative of MicroPython.  See the what is MicroPython guide for a more detailed look at the differences between CircuitPython and MicroPython.

We have a full beginner guide with tons of details on how to install, use, and code in CircuitPython for your ATSAMD21-based board here: