The ESP8266 is a low cost WiFi module capable of adding WiFi functionality to an existing microcontroller project via a UART serial connection.
The module can also be configured to act as a standalone WiFi connected device.
The ESP-07 model has GPIO0/2/4/5/12/13/14/15/16 and features a built-in ceramic antenna as well as an external U.FL antenna connection.
IMPORTANT! This is a 3.3V module, which requires a 3.3V input voltage and 3.3V logic level inputs. 5V will very likely damage this device.
NOTE: Due to the non-standard pin spacing on this module, we highly recommend the ESP8266 Breadboard Adapter PCB.
ESP8266 Specifications: https://mklec.com/pdf/ESP8266_Specifications_English.pdf
ESP8266 Modules: http://www.esp8266.com/wiki/doku.php?id=esp8266-module-family