This is the new development board from Adafruit, its to be a new standard for portable microcontroller cores.
The Feather 32u4 Basic Proto, it has a bunch of prototyping space built right in.
At the Feather 32u4's heart is a ATmega32u4 clocked at 8 MHz and at 3.3V logic. This chip has 32K of flash and 2K of RAM, with built in USB so not only does it have a USB-to-Serial program & debug capability built in with no need for an FTDI-like chip, it can also act like a mouse, keyboard, USB MIDI device, etc. This chip is well supported in the Arduino IDE and can run just about every sensor/library out there.
To make it easy to use for portable projects, a connector is added 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. The battery is tied thru a divider to an analog pin, so you can measure and monitor the battery voltage to detect when you need a recharge.
Specifications
ATmega32u4 @ 8MHz with 3.3V logic/power
3.3V regulator with 500mA peak current output
USB native support.
20 GPIO pins
I2C, SPI support
8 x PWM pins
10 x analog inputs
Built in 100mA lipoly charger with charging status indicator LED