Adafruit (PID 3505 Metro M0 Express - Designed for CircuitPython - ATSAMD21G18

Not only can you use CircuitPython, but the Metro M0 is also usable in the Arduino IDE.

Native USB, there's no need for a hardware USB to Serial converter as the Metro M0 has built in USB support. When used to act like a serial device, the USB interface can be used by any computer to listen/send data to the METRO, and can also be used to launch and update code via the bootloader. It can also act like a keyboard, mouse or MIDI device as well.

Four indicator LEDs and one NeoPixel, on the front edge of the PCB, for easy debugging. One green power LED, two RX/TX LEDs for data being sent over USB, and a red LED connected. Next to the reset button there is an RGB NeoPixel that can be used for any purpose.

2 MB SPI Flash storage chip is included on board. You can use the SPI Flash storage like a very tiny hard drive. When used in Circuit Python, the 2 MB flash acts as storage for all your scripts, libraries and files. When used in Arduino, you can read/write files to it, like a little datalogger or SD card, and then with our helper program, access the files over USB.

Comes fully assembled with headers, tested, and with the UF2 bootloader loaded on. We also include 4 rubber bumpers to keep it from slipping off your desk. No soldering required to use, plug and play!