An ATMega328P microcontroller and as much easily accessible I/O as possible crammed into 1 square inch. Requires some sort of USB to UART cable. UART pins are connected to programming UART pins. All UART/SPI/I²C pins are data pins by default and need to be configured. VCC = 5V. AREF is not connected to anything and needs to either be connected to a stable reference voltage or to VCC directly or through a smoothing capacitor. I have not ordered any parts or the boards yet but I do plan to.