The Arduino Gemma is a microcontroller board made by Adafruit based on the ATtiny85. It has 3 digital input/output pins (of which 2 can be used as PWM outputs and 1 as analog input), an 8 MHz resonator, a micro USB connection, a JST connector for a 3.7V battery, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a battery to get started.