SimPy

It is released under the GNU Lesser GPL (LGPL), starting with version 1.5.1 (previous versions were released under 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 native standard Python random module.