Wifi Module

The ESP8266 WiFi Module is a SOC with integrated TCP/IP protocol stack that can give any microcontroller access to your WiFi network. This module is capable of either hosting an application or offloading all Wi-Fi networking functions from another application processor. Each ESP8266 module comes pre-programmed with an AT command set firmware. You can simpy connect this with your microcontroller and connect to Wi-Fi right out of the box. Connecting with Arduino is much simpler and works similar to a Wi-Fi shield except that this is in a much smaller package. The module is an extremely cost effective board with a huge supporting community.
ESP8266 WiFi Module also has a powerful enough on-board processing and storage capability that allows it to be integrated with the sensors and other application specific devices through its GPIOs with minimal development up-front and minimal loading during runtime. The high degree of on-chip integration allows for minimal external circuitry. The module supports APSD for VoIP applications and Bluetooth co-existance interfaces and contains a self-calibrated RF allowing it to work under all operating conditions without any external RF parts.
There is a lot of information on ESP8266 over the web provided by amazing community support. If you are thinking of IOT, think ESP8266 modules.
Note: The ESP8266 Module is not capable of 5-3V logic shifting and will require an external Logic Level Converter. Please do not power it directly from your 5V dev board.