All things physical computing. Snap4Arduino, MicroBlocks, Hummingbird, micro:bit, Sphero, LEAP motion, you name it!
Is plain Arduino allowed?
(Arduino Error - #12 by 348663451y)
Is plain physical computing allowed?
do you connect the micro:bit to your computer with some kind of a lead, or is it wireless?
Wireless. Bluetooth I believe.
Well, it depends what you're using it for. I use a USB cable to program it.