At the Feather M0's heart is an ATSAMD21G18 ARM Cortex M0 processor, clocked at 48 MHz and at 3.3V logic, the same one used in the new Arduino Zero. This chip has a whopping 256K of FLASH (8x more than the Atmega328 or 32u4) and 32K of RAM (16x as much)! This chip comes with built in USB so it has USB-to-Serial program & debug capability built in with no need for an FTDI-like chip.
To make it easy to use for portable projects, we added a connector for any of our 3.7V Lithium polymer batteries and built in battery charging. You don't need a battery, it will run just fine straight from the micro USB connector. But, if you do have a battery, you can take it on the go, then plug in the USB to recharge. The Feather will automatically switch over to USB power when its available. We also tied the battery thru a divider to an analog pin, so you can measure and monitor the battery voltage to detect when you need a recharge.
Here's some handy specs! Like all Feather M0's you get:
Measures 2.0" x 0.9" x 0.28" (51mm x 23mm x 8mm) without headers soldered in
Light as a (large?) feather - 5.3 grams
ATSAMD21G18 @ 48MHz with 3.3V logic/power
256KB of FLASH + 32KB of RAM
3.3V regulator with 500mA peak current output
USB native support, comes with USB bootloader and serial port debugging
You also get tons of pins - 20 GPIO pins
Hardware Serial, hardware I2C, hardware SPI support
8 x PWM pins
10 x analog inputs
Built in 100mA lipoly charger with charging status indicator LED
Pin #13 red LED for general purpose blinking
4 mounting holes
The Feather M0 Adalogger uses the extra space left over to add MicroSD + a green LED:
Pin #8 green LED for your blinking pleasure
MicroSD card holder for adding as much storage as you could possibly want, for reading or writing.
Comes fully assembled and tested, with a USB bootloader that lets you quickly use it with the Arduino IDE. We also toss in some header so you can solder it in and plug into a solderless breadboard. Lipoly battery, MicroSD card and USB cable not included (but we do have lots of options in the shop if you'd like!)