The Arduino Yún is a microcontroller board based on the ATmega32u4 and the Atheros AR9331. The Atheros processor supports a Linux distribution based on OpenWrt named Linino OS. The board has built-in Ethernet and WiFi support, a USB-A port, micro-SD card slot, 20 digital input/output pins (7 of them can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, an ICSP header, and 3 reset buttons.
NB : In some countries, it is prohibited to sell WiFi enabled devices without government approval. While waiting for proper certification, some local distributors are disabling WiFi functionality. Check with your dealer before purchasing a Yún if you believe you may live in such a country. If you wish to disable WiFi, run this sketch.
The Yún distinguishes itself from other Arduino boards by its ability to communicate with the Linux distribution onboard, offering a powerful networked computer with the ease of an Arduino. In addition to Linux commands like the cURL, you can write your own shell and python scripts for robust interactions. The Yún is similar to the Leonardo with the ATmega32u4, except that it has Linux on board. (has built-in USB communication, eliminating the need for a secondary processor).