Fans of simulation games and people with God complexes will particularly enjoy Aurora alpha, a universe simulation game. Start with nothing but a sun and a particularly dense asteriod belt and end up with a universe one can be proud of.
The aim of Aurora is to create a universe teaming with life. Out of dead asteroid fields one creates planets by clicking and holding the left mouse button, which creates a gravity well. When asteroids collide, the energy released in their collision creates bigger planets... and new life.