TemPIC
This is another of those fun projects done with friends.
A friend came into possession of a box full large (200mm) 4 digit 7-segment displays with a PIC processor to drive them. After some discussion we decided to make wall thermometers out of them. He attached a button and a temperature sensor and I threw together some code and we had something to display current, maximum, minimum and average temperature which could be seen anywhere in the room. Christmas presents sorted!