WIFI Witty / Gizwits ESP-12F module, we have 50+ posts talking about getting up and running http://www.esp8266.com/u/witty @Arduino @ESP8266 @esp82662
I love these little modules. I fitted one into a friend’s model diesel locomotive. It fits perfectly. Now he has a WiFi locomotive. Removed the bottom section and plugged in headers that connect to the drive electronics and manage the lights.