Welcome to the distant future at the mark of the apocalypse.
You are a genius inventor who specializes in Physics, Mathematics and Engineering, among other things. You are also the last surviving remnant of your race. Everyone else died in a nuclear apocalypse, but you survived because your genius intellect allowed you to protect yourself. However, no one else was that lucky.
Alone, you stand in a wasteland with nowhere to go and nothing to do. Your life flashes before you, and you remember all of your past inventions. One failed invention crosses your mind. Eureka! The earlier nuclear blasts give you the answer to your invention's failure. Not only that, this invention could undo the horrifying apocalypse.
But now you realize it's going to take a long time to complete your invention. You search the globe for materials, tools and sources of power. After a year of digging, designing and construction, your invention is finally complete.
Oh, the beauty of it!
The world's first working time machine.
Though the machine works, it only serves a single, simple function. It can only send you back to exactly after the apocalypse, and it can only be used once. Sadly, your greatest invention can't be shared with the rest of the world.
But, wait! Perhaps it can still be of use to you!
You arm the machine and jump inside.
It sends you rushing back to the past, where you land alongside your past self. Your past self is shocked and amazed. After seeing what it can do, he wants to go and build the time machine. Off he speeds away to begin his quest.
You think that maybe great minds think alike and you should just wait until a third or perhaps a fourth of yourself comes from the future.
After a couple of hours, you get bored and decide to build something. Off you go to search for materials!
...Is the basic idea leading up to the game concept I thought of recently.
Essentially, the gameplay consists of a 'year' going by, during which you build something and then go back in time a year and repeat. Each time you go back, you've made another copy of yourself that builds again what you built before.
Through several time travel trips, you build a thriving metropolis (perhaps even a world or universe) made up of copies of yourself.
You spend each year either learning a skill or building something. As such, another copy of yourself fills every role in the society. From architect to farmer to policeman.
You can even create advanced surgeons that can change your gender, thus making it possible to get pregnant and have children.
Perhaps even build a cloning machine to clone yourself.
Anything is possible!
If you get really old, you build a machine that rejuvenates you and makes you younger.
The point is, you start from nothing, and using time travel, you repopulate the Earth and rebuild society even though you are the last remaining human on Earth.
Perhaps the final goal of the game is to build a time machine that goes far back enough to prevent the apocalypse.
I'm not sure how exactly the game mechanics would work or what would make it fun, but there you go. MIND VOMIT!