This is the first pre-release of MicroPython for SAMD21x18 boards including the Arduino Zero (available from Adafruit) and Adafruit Feather M0 Bluefruit LE.
See here for flashing instructions.
This first pre-release supports REPL over USB (native USB for the Arduino Zero), digital IO, time, and analog IO.
Here is how to flash an LED. Type in each line separately and make sure to match the indentation.
import machine
import time
led = machine.Pin("D13", machine.Pin.OUT)
for i in range(100):
led.value(i % 2 == 0)
time.sleep_ms(200)
After typing the last line you will get another indented line, simply hit backspace to delete the indentation and hit enter to start the flashing.