Yun Shield is one of the most powerful shields for Arduino Board. Yun Shield is designed to solve the Internet connectivity and storage issue for Arduino Board. It provides a linux system, WiFi, Ethernet and USB (can used for camara, storage, 3G etc) to Arduino.
Yun Shield runs Open Source OpenWrt system (Same system as runs in Arduino Yun) and it is fully compatible with Arduino IDE v1.5.4 or later. Yun Shield is the ideally choice for Arduino Projects which require various internet connections and more storage.
Basically, Yun Shield + Leonardo equally to the official Arduino Yun, but Yun Shield is more flexible because it can works with other Arduino board such as Uno, Duemilanove, Mega etc. And Yun Shield use external wifi antenna which provides stability and possibility for various environments.
Open source Linux (OpenWrt) inside
Low power consumption
Compatible with Arduino IDE 1.5.4 or later, user can program, debug or upload sketch to Arduino board via Arduino IDE.
Managed by Web GUI, SSH via LAN or WiFi
Software upgradable via network
Built-in web server
Support internet connection via LAN port, WiFi or 3G dongle.
Support USB flash to provide storage for Arduino projects.
Failsafe design provides robustly system.
Compatible with Arduino Leonardo, Uno , Duemilanove, Diecimila, Mega.
Processor: 400MHz, 24K MIPS
Power Input: 4.75v ~ 23v via Arduino VIN pin
150M WiFi 802.11 b/g/n
External Antenna via I-Pex connector
1 x 10M/100M RJ45 connector
1 x USB 2.0 host connector, used for USB storage or 3G connection
1 x Reset button
Compatible with 3.3v or 5v I/O Arduino.
For more detailed information, please visit the wiki.
If you need a YUN shield, you can get one here.