In terms of agents Teconic has created a simulation of ants locating food, and leaving a pheromone trail for other ants to follow. The movie below details the simulation and provides an interesting insight into the possibilities for agent based modelling in Second Life:
In terms of city creation and architecture the scripting language is increasingly being used to create modular 'out of the box' solutions. The latest of which is designed to allow users to set up a small urban centre in under 30 minutes using 'Sim in a Box' a system which allows over 4 million possible outcomes due to its modular nature.
The movie below details the simulation:
We will be taking a close look at the Second Life Scripting Language for both agent based modeling and architectural components over the coming weeks.