There has recently been a huge influx of extremely small dev board based on the ATtiny85. This small 8-pin microcontroller is able to run most Arduino sketches, and the small size and low price ...

Update April 2022: also works on clone of SparkFun Pro Micro ... defined Arduino pin int TXLED = 30; // The TX LED has a defined Arduino pin // the setup function runs once when you press reset or ...