Building an app for winter sports. You can download the map for a ski resort, and use the map to see where individuals in your group are, and suggest meetups (summits) on the map, and everyone gets a personalized route generated to that point.
Add in some evolutionary strategies, and you have the recipe for a good sci-fi book: a fungus in Chernobyl rapidly outpaces its competitors due to its ability to absorb radiation. Each iteration grows and reproduces faster, until it is so blindingingly fast that it begins to outpace the output the fuel rods produce.
The world rejoices as this fungus is perfect for cleaning up nuclear waste products, until we realize that it evolved to function outside of Chernobyl and begins to eat everything it can reach. Mankind launches into a desperate struggle for survival as the fungus lays waste to large swathes of land.