Image courtesy of Adafruit
The Adafruit METRO 328 is functionally identical to the Arduino Uno, and can be used for all projects that call for the Arduino Uno in the Exploring Arduino book. The MCU on the METRO 328 is the ATmega328. The board has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a micro USB-B connection (different from the Uno’s full-sized USB-B connection), a power jack, an ICSP header, and a reset button. You can learn more about the specifications of the Adafruit METRO 328 on Adafruit’s product page.