An Arduino Pro Mini is a small microcontroller derived from the Arduino Uno using the ATmega328. It is unique for its tiny size and the required external FTDI adapter.
Arduino Pro Mini is a microcontroller board based on the ATmega328. With 14 digital IO pins, 8 are analog inputs, 6 digital pins capable of PWM output. Programming and power is done via a six pin header which can be connected to a FTDI cable. The official board was designed and is manufactured by SparkFun Electronics, however there are many clones out there. It exist both 5V/16MHz and 3.3V/8MHz. It can be used with UART, SPI and I2C.