SimPy (= Simulation in Python) is an object-oriented, process-based discrete-
event simulation language based on standard Python and released under the GNU
GPL. It provides the modeler with components of a simulation model including
processes, for active components like customers, messages, and vehicles, and
resources, for passive components that form limited capacity congestion points
like servers, checkout counters, and tunnels. It also provides monitor variables
to aid in gathering statistics. Random variates are provided by the standard
Python random module.

WWW: http://simpy.sourceforge.net/