The Arduino YÚN is the combination of a classic Arduino Leonardo (based on the Atmega32U4 processor) with a WiFi system-on-chip running OpenWrt-Yun (a GNU/Linux distribution based on OpenWrt). We embedded the Linux machine directly on the PCB of the Arduino Leonardo and we connected the two so that from Arduino it's very easy to run commands on the Linux side and use it as an Ethernet and WiFi interface.