In a true madmax world steam is king. I have always wanted a hotbulb engine that could run on anything flammable liquid or gas as long as it can be put in the bulb it goes bang..pppfffttt bang pppfffttt with leather belts on the power take off all 1850s tech.
The steam turbine dates from the 1880s, and we wouldn’t have AC power without it. Still lots of cargo ships in service that are powered by steam turbines too. And of course, nuclear vessels use them.
Used to be website, Mike Brown Solutions sold small steam engines and plans for power systems. The site is gone but you stll see a few sites that discuss his steam plants.
There’s an old steam tractor on YouTube that takes on new tractors in pulling contests. It has something like 19 HP and 12000 ft pounds of torque. It wins.
When I was a kid, a guy down the street built a steam powered Plymouth. He cleaned up every construction site around, making chunks out of scrap lumber, for fuel.