<p>I would like to know what kind of toolkits, languages, libraries exist for agent-based modeling and what are the pros/cons of them?</p>

<p>Some examples of what I am thinking of are
<a href="http://www.swarm.org" rel="noreferrer">Swarm</a>, <a href="http://repast.sourceforge.net/" rel="noreferrer">Repast</a>, and <a href="http://www.aitia.hu/services_and_products/simulation_systems/mass" rel="noreferrer">MASS</a>.</p>

I got introduced to
Dramatis
at OSCON 2008, it is an Agent based framework for Ruby and Python.  The author (Steven Parkes) has some references in his blog and is working at running a language agnostic
Actors discussion list
.
This page
at erights.org has a great set of references to, what I think are, the core papers that introduce and explore the Actors message passing model.