The following is just a list of ideas. Even better if you come up with something on your own!
Lego with micro controller - https://youtu.be/d8EX05wC9XY
Makey Papercraft - https://www.thingiverse.com/thing:2920325
Waving Makey - Papercraft - https://www.youtube.com/watch?v=l9SLMLViJng&feature=youtu.be
NeoPixel something: I have many shapes, circular, matrix, ...
Automatic door with distance and servo:
https://shop.tinkergen.com/media/wysiwyg/product_media/BitGadgetKit/file_3.png
Micro:Bit smartphone camera remote:
https://maker.pro/microbit/projects/build-a-bluetooth-selfie-remote-for-your-smartphone-using-microbit
Frustration:
https://projects.raspberrypi.org/en/projects/frustration
Burglar Alarm
https://www.hackster.io/anish78/create-remote-burglar-alarm-using-bbc-micro-bit-7f7ee7
Micro:Bit Bus
https://www.hackster.io/gpteacher/microbit-bus-robot-car-025057
Mirco:Bit football
https://make.techwillsaveus.com/microbit/activities/microfootball
Temperature Gauge
https://www.hackster.io/anish78/how-to-create-temperature-gauge-using-micro-bit-a601cc
Milk Carton Robot
https://makecode.microbit.org/projects/milk-carton-robot
Railway Crossing
https://makecode.microbit.org/projects/railway-crossing
Micro:Bit Tetris, but with Neopixel Matrix! Who likes to solder!
https://www.101computing.net/bbc-microbit-tetris-game/
Micro:Bit stop light:
LEDs for the 3 lights and Micro:Bit counting down for the walk signal
Reciprocating Rack and Pinion - https://www.thingiverse.com/thing:3038784
WiFi Weather Station - https://www.thingiverse.com/thing:1944905
Otto DIY+ - https://www.thingiverse.com/thing:2786066Â
Juno Rover - https://www.thingiverse.com/thing:1720394
EEZYbotARM MK2 - https://www.thingiverse.com/thing:1454048
Sound activated motors - https://www.youtube.com/watch?v=h-pKfdNgQkI&feature=youtu.be
Tightrope Unicycle Bot - https://www.youtube.com/watch?v=enue1hJHv_E&feature=youtu.be
Robot hand - https://www.youtube.com/watch?v=0hbAXvNgJEg&feature=youtu.be