A Bitty Software application - http://www.bittysoftware.com
bitty controller lets you remote control a BBC micro:bit connected device like a 4tronix Bit:Bot or a Kitronik buggy or MOVE mini. It provides a choice of user interfaces including a classic dual d-pad controller, an analog touchpad for fine control and an enhanced UI which includes support for up to 5 sensors and has an extra button.
The Bitty Software web site contains code examples and further information.
Note that Bitty Controller replaces the old Bitty Game Controller, which is no longer available.
And if you're feeling adventurous, be aware that bitty controller can be used with any microcontroller which implements the BBC micro:bit's Bluetooth Event Service. More information can be found at http://www.bittysoftware.com.