I recently bought an Adafruit Feather M0 board. On Arduino IDE's board manager, I found and installed the Arduino SAMD boards I can't find the Adafruit SAMD package as explained here:
Any idea why this add-on does not show up on the list ? I am using the latest version of IDE, i.e. 1.8.2, I also tried with 1.6.4 with the same success...
After doing that open Tools > Boards Manager, wait for downloads to complete, and you will see Adafruit SAMD Boards in the list and you can install it.