either have a chip capable of USB or rely on a V-USB implementation, the old fogies of the Arduino world, the Uno and Mega ... this version is a real bootloader for the ’16u2 that replaces ...

which offers a ATmega328 microcontroller with Optiboot (UNO) Bootloader. The Metro 328 has been created to provide extra features on top of what you would expect from the Arduino Uno offering ...