Looking for a game (or maybe a sandbox) with heavy AI/ agent modelling aspect

Maybe I'm not looking for a game but some sort of simulation software. Basically looking for something that, either natively or through mods, would allow me to fiddle around with AI or agent modelling. Preferably something that would allow me to go so far as to write my own scripts.

I'm envisioning a world-game like Civ, but open to any suggestions. Thanks!