The Stirling engine is an external combustion engine invented in 1816 by Robert Stirling. He came up with this engine design because he was concerned about safety. The steam engine in its early years would sometimes explode and cause injuries.
The Stirling engine can be quieter and more efficient than the steam engine, and it is able to run on nearly any heat source — which means it is compatible with alternative and renewable energy sources.
Interested in getting hands-on with this interesting engine? Here are some Stirling engine builds to get you started.