Toppled Towers is a simulspace game, given players freedom to act as they please in a post apocalyptic environment. Players typically do their best to survive as long as possible, battling the elements and each other.
The simulspace was designed and created as part of a social science grant; in fact, the primary purpose of the simulspace is to serve as the basis for social experiments. Most players would join together for survival, providing data on various types of social arrangements. Occasionally designers of new consumer technologies or augments have arranged for functionally similar devices to be introduced into the game to see how they will be used, and the simulation is realistic enough that inventions first created in the game have been turned into real devices.
Originally, the environment was explicitly a post-apocalyptic Earth, but after the Fall all landmarks were removed and the game now takes place on an Earth-like planet. There has been a dramatic dip in popularity, but a core of loyal players has remained, most newly focused on rebuilding.