Diaspora includes a few examples of this as well. Mathematical discoveries can only be made in the "mines", and people install these mods to make them better at

Diaspora includes a few examples of this as well. Mathematical discoveries can only be made in the "mines", and people install these mods to make them better at mining, after working through some of the beginner steps unaltered to see if they'd like it. There's also a mod that explicitly prevents you from ever uninstalling it; I don't remember what else it even did, it seemed to spread like a slow virus through the artistic communities in the simulation.