ESP8266 is a great small WiFi module that carries a microcontroller programmed to do basic IO controls. Having WiFi functionality gives several possibilities to access modules remotely to control things within reach of your network coverage. Rui Santos suggests building a simple Android app used as a control panel for the ESP module.
In his tutorial, he goes through the necessary steps of programming the ESP8266 module with LUA script and building an Android application with MIT App Inventor. App Inventor is very easy to use, and you can create simple applications within an hour. The app-building consists of GUI designed and visual code blocks (similar to scratch on Raspberry Pi). In his example, he demonstrates how to control two LEDs from the Android app. The code can be easily expanded for more functionality if necessary.