Now a days robotics is one of the major field of science . Most of the robots can be made easily with arduino microcontroller .Arduino microcontroller is easy to use than pic or any other microcontroller. One of the reason is that it uses C language for compilation and most of the libraries are already built in the compiler.
Using Arduino with Android has many Application some them are mention below
1) Android Controlled CAR
2) Arduino Android Weather Station
3) Home Automation System
4) Line following Robot

This Apps encourage the user to make these type of demanding projects.