Control the weather on a planet
You Are God is a game that allows you to take on the role of the God of a single planet. You are in control of the planet's weather, but you do not have control of the planet's life. Everything you do affects any plants, animals or even people that develop on your world. A storm may bring much needed cool rain, but it could also scare inhabitants or kill life if it is too strong.
In You Are God, you [the player] must care for a new planet. Warm the planet with sunlight and wet it down with rain to produce the best conditions for life to develop. If the conditions are right, plant life may develop. If there is plant life, it's possible that animal life may form. Once there is animal life, it may develop sentience. Once this happens the lifeforms will create a new religion to offer solace to their fears and desires.
Will they worship you, or will they come up with a different God? Will the different nations turn on each other, fighting over which religion is correct, or will they unite in harmony and develop new technologies together? Will they become advanced enough to journey into space and potentially leave the planet entirely? They will live their lives, following their own free will, but you must guide them and care for them if they are to reach their full potential.
There are three continents (nations) that grow and run by their own sets of rules. These rules are dictated by the religion they design and follow. If you are the God they worship, you will have more influence over them, but you can never control them. If you are unknown or despised by the people they may turn against you. If the nations have different Gods, they may fight and could even destroy the planet in the process.
The endgame idea is for the people on the planet to discover another world and leave their home planet behind. As the technology level rises, the people will notice the stars, go to space, colonize the moon, research other planets and eventually leave to colonize on another world. Of course, it's also possible to keep them on the planet and under your care with religious influence.