1. Support for the Arduino IDE 1.0+ (OSX/Win/Linux).
2. Power via USB or external source—5V or 7–16V (automatic selection).
3. On-board 150mA 5V regulator.
4. Built-in USB (and serial debugging).
5. Six I/O pins (two are used for USB only if your program actively communicates over USB; otherwise, you can use all six even if you are programming via USB).
6. 8k flash memory (about 6k after bootloader).
7. I2C and SPI (via USI).
8. PWM on three pins (more possible with software PWM).
9. ADC on four pins.
10. Power LED and test/status LED