Datasheet

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 - 5.7 grams

ATSAMD21G18 @ 48MHz with 3.3V logic/power

256KB of FLASH + 32KB of RAM

No EEPROM

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

Power/enable pin

4 mounting holes