Writing Traffic Light simulators is a excellent educational tool.

Learners can start off simply by just creating and programming one traffic light.

Once that has been acheived and then learners can go onto extra tasks suchs as turning it into a pedestrian crossing simluator and adding a red/green person (or walk/dont walk) light

Then a button can be added - then a wait light - and beeping sound etc

Further development can be added by simulating a person crossing a road and even have cars driving around responding to the signals

It is a classic low barrier for entry - high ceiling project