While it’s not really very complete, Energy Tycoon has come quite a long way in production and polish without seeming to catch much attention.
There’s only the one map and one mission, plus the tutorial stages themselves, and the translation is incomplete in a few minor details but actually the whole thing looks quite promising and you could while away a couple of hours with what’s there.
It’s rare to see an open-source project go so far with so little fanfare.
Build and research a variety of energy-generation technologies, use public-relations to increase your customer-base, green-washing to bamboozle the public, or illegal dumping to cut costs. Mine and/or trade in natural gas, coal, or uranium rods. Adjust customer contracts to keep your operation funded.
Energy Tycoon is open-source software (mostly, but is nevertheless free-of-charge), and has binaries available for Windows and Debian Linux. The source-code is available for other platforms.