Arduino Yún is the combination of a classic Arduino Leonardo (based on the Atmega32U4 processor) with a Wifi system-on-a-chip running Linino (a MIPS GNU/Linux based on OpenWRT). It’s based on the ATMega32u4 microcontroller and on the Atheros AR9331, a system on a chip running Linino, a customized version of OpenWRT, the most used Linux distribution for embedded devices.
Like a Leonardo, it has 14 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator and a micro USB connector.
Like any modern computer, it’s Wi-Fi enabled, it has a Standard-A type USB connector to which you can connect your USB devices and it has a micro-SD card plug, for additional storage.
For more information about the Arduino Yún, see the product page.