I would like to know what kind of toolkits, languages, libraries exist for agent-based modeling and what are the pros/cons of them? Some examples of what I am thinking of are Swarm, Repast, ...

I've encountered the term "multi-agent computing" as of late, and I don't quite get what it is. I've read a book about it, but that didn't answer the fundamental question of what an agent was. Doe...