The Arduino Yún is a microcontroller board based on the Atmel ATmega32u4 and the Atheros AR9331.
The Atheros processor supports a Linux distribution based on OpenWRT named Linino. The board has built-in Ethernet and WiFi support, a USB-A port, micro-SD card slot, 20 digital input/output pins, a 16 MHz crystal oscillator, a micro USB connection, an ICSP header, and a 3 reset buttons.
Additional info: http://www.ckuehnel.ch/dokuwiki/doku.php?id=arduino_yun
For porting older Arduino sketches to IDE V. 1.0 and higher look to [Porting]
I wrote books covering Arduino Yún and Dragino Yún Shield in German and English.