MATSim provides a toolbox to implement large-scale agent-based transport simulations. The toolbox consists of severel modules which can be combined or used stand-alone. Modules can be replaced by own implementations to test single aspects of your own work. Currently, MATSim offers a toolbox for demand-modeling, agent-based mobility-simulation (traffic flow simulation), re-planning, a controller to iteratively run simulations as well as methods to analyze the output generated by the modules.
MATSim
A toolkit for building multi-agent transport simulations.

- Fast Dynamic and Agent-Based Traffic Simulation
Simulate whole days within minutes - Private and Public Traffic
Both private cars and transit traffic can be simulated - Supports Large Scenarios
MATSim can simulate millions of agents or huge, detailed networks - Versatile Analyses and Simulation Output
E.g. compare simulated data to real-world counting stations - Modular Approach
Easily extended with your own algorithms - Interactive Visualizer
See what each agent is doing during the simulation - Open Source
You get the Java Source Code, which runs on all major operating systems - Active Development
New features are constantly being added and current ones are improved
Some examples of scenarios in which MATSim has been used are listed below.