The micro:bit is an open source system originally designed by the BBC for use in computer education in the UK and is now available in Australia.
Described as being about half the size of a credit card, you can use the accelerometer to detect movement and tilting or the magnetic sensor to detect metal or create a compass. Uses for the 5 x 5 LED display are limited only by the imagination and 2 on-board input push buttons provide instant control.
Another 3 inputs are provided via the 5 ring connectors (the other 2 are for power and ground) which can be accessed via alligator clips or banana connectors. On top of this, the ring connectors form part of a larger 23 pin edge connector for more advanced projects. And if that isn't enough, USB and Bluetooth® connectivity allows interfacing with other peripherals!
Programming can be done via Microsoft MakeCode or MicroPython, both of which are available on the micro:bit foundation website.
Power is via USB or the provided 2 x AAA battery holder (batteries included).