The SparkFun ESP8266 WiFi Shield is an Arduino compatible shield for the ESP8266 WiFi SoC a leading platform for Internet of Things (IoT) or WiFi-related projects. There are a variety of designs based around the ESP8266, including tiny, modular boards and more accessible development boards like our very own SparkFun ESP8266 Thing. The ESP8266 WiFi Shield finds a middle ground between the Module and the Thing that provides a great introduction to the ESP8266 without leaving the comfortable hardware confines of your Arduino.
The ESP8266 WiFi Shield comes pre-flashed with an AT-command firmware, so it can be controlled by any UART, but it also breaks out and provides command access to all of the ESP8266s I/O. Since this is an Arduino shield, it makes it easy to attach to any development board that utilizes the Arduino R3 layout. All it will take is a little soldering to attach the necessary headers. The ESP8266 is much more than a simple serial-to-WiFi gateway. It has almost a dozen I/O that can be configured as digital inputs or outputs it even has an ADC.
Key Features

Arduino R3 Layout

802.11 b/g/n

Wi-Fi Direct (P2P), soft-AP

Integrated TCP/IP protocol stack

Integrated TR switch, balun, LNA, power amplifier and matching network

Integrated PLLs, regulators, DCXO and power management units

Integrated low power 32-bit CPU could be used as application processor

+19.5dBm output power in 802.11b mode

Resources

Schematic

Eagle Files

Hookup Guide

AT Command Set

GitHub(Design Files)

GitHub(AT Arduino Library)

ESP8266 Powered Propane Poofer
Internet of Things Experiment Guide