The BBC micro:bit is a piece of electronics, that is half the size of a credit card. You can program it by plugging it into a computer USB port, or mobile device with bluetooth. The micro:bit supports Windows, Mac, and Linux (including the Raspberry Pi). It's super easy to write code in your browser or an editor, using visual or text programming!
It has a light display powered by 25 LEDs as well as sensors for movement (gestures), magnetism, temperature, with 2 buttons and they communicate with each other using radio. For more information see the official page.