My tenth idea comes from a series of songs written by ELO called
Prologue, Twilight, and Yours Truly 2095
You are an ordinary person who lives a relatively ordinary life in your perfectly ordinary city. But one day, you receive a phone call. The person on the other end of the phone tells you that you, and a group of other such ordinary individuals are to save the world, or at least, most of it. Technology is about to advance: there will be hovercars, androids, rocket ships going to Mars are about to be invented. But little do they know that advancement will give rise to a threat that may very well spell doom for the human race and the planet earth.
This is when you recognize the voice on the other end of the phone. It's you, from another time. You originally failed in your task, and your planet is in ruins. Everyone has given up. Everyone has submitted. Except you and your friends, whom you likely haven't met yet. This is their last hope.
You are their last hope, that now you can use this knowledge of future events to prevent calamity. The voice thanks you for your time, and hangs up. It's time to get to work.
I've left a few things open here, such as what this calamity actually is. Is it a robot army? Do aliens invade the planet for your technology and resources? Does nuclear war break out? And how do you, a completely normal person plan on stopping this. I'd likely take a poll, or have people post their ideas, and then go from there.