If you're going to bother tackling a craft project, it might as well do something interesting when you're done with it. Aliaksei Zholner used his skills with paper and glue to build a working Stirling engine powered by a bowl of hot water and a handful of ice cubes.
Even the flexible diaphragms that move the pistons up and down are made from reinforced tissue paper, but how can the creation run for almost 13 minutes on just water? It wouldn't with just tepid water from the tap, but the temperature difference between the hot water in the bowl underneath and the frozen ice cubes causes air in a sealed cylinder to move back and forth as it warms and cools. That movement then powers the cylinders of this simple motor, which turns the wheel.
Is it useful for much more than a fun toy to place with on your desk at work? Not really, but what other reason do you need to try and build your own between meetings?