It's blue! It's skinny! It's the Arduino Pro! SparkFun's minimal design approach to Arduino. This is a 3.3V Arduino running the 8MHz bootloader. Because the system voltage for this board is lower than other Arduino development boards, it may not be compatible with many Arduino shields which were designed to run at 5V. The Arduino Pro 3.3V still works great with our prototyping shield so you can create your own 3.3V shields. The lower system voltage also has its advantages, like ease of use with many common 3.3V sensors.