It's ESP-12 (ESP8266 WiFi module) on breakout board, with all I/O pin accessible. Bought from China TaoBao (淘寶) market, cost RMB ¥15.00/pc :)
(have to solder the ESP-12 on breakout board by myself)
Test with example of "Arduino Due + ESP8266 - to Join AP".
My first exercise of using ESP-12:
- Arduino Due + ESP8266: Web Control LED