Have thought about basic concepts for fiction that let you start with an Earth-like place that is not here. And recently gave out an idea for free on my Twitter. Decided to talk out more here.
In first tweet gave broad outlines.
Free story or game idea: in a slightly distant future a restorative preserve is sending out anomalous data.
Is highly isolated for balanced ecosystem of restored flora and fauna of Earth, so an investigative team must be minimally invasive.
Solve the mystery. Explain anomalies.
Second tweet handles a bit more.
The restorative preserve is a station built on a small planetoid with artificially normal Earth gravity.
Is shielded from most radiation from its blue sun to mimic that of Earth.
The investigative team soon discovers impurities. Some other humans have invaded against the rules.
Can actually just copy out to use as a prompt with emergent AI to more fully develop initial story idea. Make changes of course, as you like.
For example can drop part about humans invading. I did that just to make a tad bit easier if wish for an easier writing start.
Note: energy can be simply provided by blue star which would be way more powerful than our Sun. So protective shields are required, and also hold in atmosphere. Panels would capture that energy as needed.
Would be very technically sophisticated future humans able to construct such a useful planetoid pulling needed materials together, like to have required levels of water and salt. Plenty of such is in space and readily available. Way more in space than on planets like here on Earth.
And finally artificial gravity is necessity. As a fiction concept I think that is common, and do not have to explain technical ideas to remain well within sci fi expectations.
The nostalgia aspect appeals to me and allows for small teams as well as having a pristine quality. Human impacts are to be kept at a minimum on any preserve. And yeah can assume there are multiple ones, possibly echoing back different ecosystems of Earth.
