An ATmega328 in DIP package, pre-loaded with the Arduino Optiboot Bootloader.
This will allow you to use Arduino code in your custom embedded project without having to use an actual Arduino board.
To get this chip working with Arduino IDE, you will need an external 16MHz crystal or resonator, a 5V supply, and a serial connection adapter.
If you are not comfortable doing this, we recommend purchasing the Arduino Uno board online that has all of these built into the board.
It's like the ATmega168, with double the flash space.
23 I/O lines, 6 of which are channels for the 10-bit ADC. Runs up to 20MHz with external crystal.
Note: This contains the bootloader used on the Arduino Uno, with small modifications to work more reliably with different serial connection options (mainly the FTDI). Check the link below for more information.